Millions could die in Yemen in the “largest famine the world has seen for many decades”, if the Saudi Arabia-led coalition does not allow aid to enter the country, a United Nations official said on Wednesday.

On Monday, the Saudi-led faction had said it had closed all points of entry – air, land and sea – to Yemen to stop the Houthi rebels from getting arms from Iran. The Houthis had fired a ballistic missile towards the Riyadh airport on Saturday, but Saudi forces had intercepted it.

The UN said access to humanitarian aid, which was not sufficient even earlier, has now worsened.

Starvation and a cholera outbreak has worsened the situation in Yemen, which has been in a state of war for the past two and a half years. Over seven million people are in need of food assistance.

“I have told the [UN Security] Council that unless those measures are lifted...there will be a famine in Yemen,” UN official Mark Lowcock said on Wednesday, according to Al Jazeera. He is the under-secretary-general for humanitarian affairs who visited Yemen in October.

“It will not be like the famine that we saw in South Sudan earlier in the year, where tens of thousands of people were affected,” Lowcock said. “It will not be like the famine that cost 250,000 people their lives in Somalia in 2011. It will be the largest famine the world has seen in many decades, with millions of victims.”

He said UN Secretary-General Antonio Guterres had spoken with Saudi Foreign Minister Adel al-Jubeir and asked the country to open access to humanitarian aid immediately.