Security forces are still engaged in an encounter with an unknown number of militants in Punjab's Pathankot, more than 13 hours after the gunmen attacked an Indian Air Force base. Four militants and three security personnel have been killed so far after the suspected Jaish-e-Mohammed gunmen entered Punjab from Pakistan, officials said.

The Indian Air Force said in a statement that the militants were detected by aerial surveillance platforms following "effective preparation and coordinated efforts by all security agencies". The statement added that intelligence inputs had been available of a likely attempt by the militants to infiltrate the military installation, reported ANI. The likely plan of the gunmen to destroy valuable assets of the Air Force has been foiled, it said.

The attack took place a week after Prime Minister Narendra Modi paid a surprise visit to Lahore to meet his Pakistani counterpart Nawaz Sharif. The two leaders had decided to resume bilateral talks and the meeting had boosted hope for a thawing of tensions between the two countries.

Pakistan condemned the attack, with its foreign ministry saying that the country "remains committed to partner with India and other countries in the region to eradicate the menace of terror". However, analysts have drawn parallels with former Indian Prime Minister Atal Bihari Vajpayee's bus trip to Lahore, which was followed by the Kargil war in 1999.

Here is a round-up of the developments so far:

4.30 pm: The Congress has said that Prime Minister Narendra Modi and the Centre will have to reassess its Pakistan strategy after terrorists reportedly from across the border attacked an Air Force base in Punjab's Pathankot.

Party spokesperson Randeep Surjewala said, "It is indeed a very serious matter as seven days after PM Modi visited Pakistan to meet his counterpart Nawaz Sharif, a terrorist module comes from Pakistan and attacks our frontline security installation."

Surjewala added that the attacks proved that Pakistan's Inter-Services Intelligence "continues to sustain and support terror activities against India" and that terror camps that are run by terrorists for carrying out anti-India activities continues to be supported by Pakistani establishments.

The Bharatiya Janata Party replied that India cannot derail the resumed dialogue with Pakistan due to "one attack" and accused the Congress of politicising the incident. Union minister Prakash Javadekar said, "Unless you talk terror, terror will not [be defeated]."

3.50 pm: Defence minister Manohar Parrikar has been briefed on the Pathankot situation by the chiefs of the Indian Army, Air Force and the Navy, and the National Security Adviser, according to reports.

3.40 pm: The Communist Party of India has condemned the attack on Pathankot air base and urged both India and Pakistan not to fall into the terror outfits' "trap of provocation" and derail peace talks. CPI national secretary D Raja also demanded that India take up the matter with Pakistan seriously and push for action against those responsible for the attack.

3.30 pm: Punjab Congress chief Amarinder Singh has condemned the Pathankot attack, saying it was a clear attempt by "rogue elements in Pakistan" to sabotage the peace process with India. He added that it was the responsibility of the Pakistani government to identify such rogue elements and deal with them with a firm hand, reported PTI.

Singh also brought up Prime Minister Narendra Modi's surprise trip to Lahore last week and said he hoped the attack was not a repeat of what happened after former Prime Minister Atal Bihari Vajpayee's trip to Pakistan. The Kargil war had taken place soon after Vajpayee's visit.

Singh lauded the security forces who engaged with the terrorists:

3.20 pm: Union Minister of State for Home Affairs Kiren Rijiju has said that the government has received credible information about the Pathankot attack being sponsored by some elements from across the border, reported ANI. Rijiju added that central agencies are working in coordination with the Punjab police in the investigation.

2.50 pm: Pakistan has condemned the Pathankot air base attack. The Pakistani Foreign Ministry said the country "remains committed to partner with India and other countries in the region to eradicate [the] menace of terror".

2.30 pm: ANI reported a loud explosion was heard from inside the Pathankot air base, minutes after it reported that no gunshots have been heard in the area for over one hour.

2.10 pm: The Ministry of External Affairs has said that the security forces' operation against the suspected terrorists is still ongoing, reported ANI. The ministry did not say anything about how the incident would affect relations with Pakistan. The statement added that the immediate focus was on resolving the situation and it is "premature to say anything more at this point".

1.10 pm: The Congress has said that the Pathankot air base attack raises security concerns for Punjab as the state has seen a sudden surge in violence after being peaceful for the last 20 years. Party spokesperson Randeep Surjewala mentioned the recent terror attacks in Gurdaspur and Udhampur, which is on the state's border with Jammu and Kashmir.

The party said the attacks raise questions about the central government's strategy for preventing such incidents. The ruling Bharatiya Janata Party, meanwhile, said that India will keep doing its best to deal with terrorism.

12.55 pm: Former Jammu and Kashmir Chief Minister Omar Abdullah said that the Pathankot air base attack was the first major challenge for Prime Minister Narendra Modi concerning Pakistan. Experts fear the attack could affect India-Pakistan relations, a week after Modi paid a surprise visit to Lahore to meet Pakistani Prime Minister Nawaz Sharif. The meeting had boosted hope for a thawing of tensions between the two countries.

12.40 pm: Fresh firing was heard in Pathankot when security forces were conducting a combing operation after killing four terrorists who attacked the Air Force base, reported PTI. More terrorists could be present in the area, the report quoted defence sources as saying.

The Indian Air Force has pressed two attack helicopters into service. The helicopters are targeting the areas from where the firing is believed to be coming from, according to the report. The security forces have also deployed drones to get the exact location of the terrorists.

PTI also reported that a Garud commando of the IAF has been killed in the encounter, taking the toll of security personnel to three, according to defence sources.

12.30 pm: Punjab has been put on alert following the Pathankot air base attack. Security was tightened across the state, reported PTI. Security has also been beefed up at Air Force Stations at Chandigarh and Halwara in Punjab and at the air base in Ambala.

Vigil has also been stepped up at Chandimandir and at Ambala Cantt.

Vehicles crossing through Army and Air Force areas were being checked by police and army personnel.

Security at railway stations of both Punjab and Haryana has also been increased, officials said.

12.15 pm: A National Investigation Agency (NIA) team has reached the Pathankot Air Force base to probe the incident, reported PTI. The Home Ministry asked the agency to keep a full investigation team ready as the case could be transferred to it, the report quoted sources as saying.

As per the standard operating procedure, an NIA team is asked to intervene when a terror strike takes place so that it can share its expertise and get first-hand information about the case.

12 pm: Home Minister Rajnath Singh on Saturday said India would give a fitting reply to Pakistan for the Pathankot attack. “Pakistan is our neighbour, we want peace, but any terror attack on India will get a befitting response,” he said, according to The Hindu.

10 am: The encounter between the militants and security personnel is over, the Punjab police said. Four militants and two Indian Air Force officials were killed in the six-hour gun battle, PTI reported.

9 am: According to Times Now, a terror module from Bahawalpur in Pakistan was behind the attack.

8.30 am: ABP News reported that an emergency meeting had been called at the Air Force headquarters in Delhi, and that Prime Minister Narendra Modi was going to be informed about the operations.

7.30 am: A group of militants believed to be from across the border attacked an air base in Pathankot, Punjab.

The attack, which started at 3.30 am, is believed to be connected with the hijacking of a an army vehicle on Friday. A group of militants had abducted the police superintendent and three others in an army vehicle and left them beaten up along the highway later in the day. The militants were reportedly roaming the area undetected for 24 hours.

Gunfire was heard from inside the air base, which contains MiG 29 fighter aircraft and helicopters. Officials suspect the strike had been perpetrated by terror outfit Jaish-e-Mohammed, which has indicated the intent to damage military property on previous occasions as well. Security forces had been warned of such an attack by intelligence personnel, officials said.

This is the second big attack by suspected terrorists in Punjab in a year. On July 27 last year, three militants opened fire in a bus and then stormed a police station in Dina Nagar, Gurdaspur, before being killed after 12-hour gun battle.