Ukraine on Sunday accused Russia of seizing three of its navy vessels off the Crimean Peninsula after firing at them, AFP reported. Ukraine said six of its soldiers had been injured, two of them seriously. But Russia’s FSB security service, which oversees the border guard service, claimed only three soldiers had suffered non-threatening injuries.

Russia claimed it had been forced to act as Ukrainian ships illegally entered its waters to “intentionally” provoke a conflict. Moscow said it used weapons “in order to stop the Ukrainian military”, AFP reported. It confirmed that “three Ukrainian navy ships were boarded and searched”.

The incident took place in the Kerch Strait, a narrow body of water that gives access to the Sea of Azov and is used by both the countries. Russia had annexed the Crimean Peninsula in 2014.

The Ukrainian Navy alleged that the attack took place when two of its warships and a tugboat were heading through the strait for Mariupol port. A Russian border guard vessel rammed its tugboat in “openly aggressive actions” and then fired at one of its ships, injuring the soldiers, said the Navy. A Russian tanker also blocked the Kerch Strait, with military aircraft flying overhead.

In September, the Ukrainian Navy had accused Russian border guards of “acts of provocation” against its ships taking the same route. Ukraine has increased the number of ships and border guard patrols in the Sea of Azov, which is accessible via the Kerch Strait.

The FSB security service said that the Ukrainian ships “illegally entered a temporarily closed area of Russian territorial waters” and that its border patrol boats seized the Ukrainian naval vessels in the Black Sea and used weapons to force them to stop.

“The purpose of these provocative actions by the Ukrainian navy is to create a conflict situation in the region,” RT quoted the agency as saying. Russian leaders also accused Ukraine of acting on the behest of its Western allies. Crimean leader Sergei Aksyonov wrote on Facebook that he “was sure the Western masters of the Kiev regime are behind this act of provocation”.

“The Ukrainian puppet authorities... are risking unleashing a large military conflict,” Deputy Speaker of Russian Parliament Pyotr Tolstoy said on Facebook. “One thing is clear: Russia won’t allow military provocations in its territorial waters.”

Ukraine said it had given advance warning of the routes its ships would follow. President Petro Poroshenko met with his senior military and security chiefs and said he would propose that Parliament impose martial law, Reuters reported. “I want to emphasise separately that we have all irrefutable evidence that this aggression, this attack on the Ukrainian Navy’s warships was not a mistake, not an accident, but a deliberate action,” he said in a statement.

The United Nations Security Council will discuss the developments on Monday at the request of Russia, Reuters quoted Deputy Russian UN Ambassador Dmitry Polyanskiy as saying.

The European Union said that it expects Russia to restore freedom to navigate via the Kerch Strait and urged both sides to act with utmost restraint to deescalate the situation, The Guardian reported. Spokesperson Maja Kocijancic said, “The EU does not and will not recognise the illegal annexation of the Crimean peninsula by Russia.”