Forces loyal to Syrian regime head Bashar al-Assad said on Wednesday that they had cut off all supply routes into eastern Aleppo, and the regime air-dropped thousands of leaflets there, asking residents to cooperate with the pro-Assad forces and calling on fighters to surrender.

Assad’s initiative comes a day after the United Nations said it hopes to restart peace talks in August.

Previous attempts at a diplomatic solution to end Syria’s five-year-old civil war collapsed in April, partly due to an uptick in violence in Aleppo.

On Tuesday, the army texted residents to ask them to leave the city and to give up their weapons.

Concern for those trapped in the opposition-held part of Aleppo is rising. The U.N. aid chief asked on Monday for weekly 48-hour pauses in fighting to allow food and aid to be delivered.

Once Syria’s largest city, Aleppo has been divided between opposition-controlled and regime-held sectors all through the civil war. Taking full control of the city would be an addition to Assad-held territory.

An advance by pro-Assad forces around the only remaining supply route into the eastern sector this month enabled them to fire on it at close range, making the battlefront Castello road too deadly to use and putting at least 250,000 people in rebel-held districts under siege.

“(Armed forces) have cut all supply routes and crossings which terrorists used to bring mercenaries, weapons and ammunition into the eastern neighborhoods of Aleppo,” a statement from the Syrian military general command said.

Assad had taken a habit out of unwarrantedly referring to all rebels as terrorists.

The Britain-based Syrian Observatory for Human Rights said eastern Aleppo had been under effective siege since July 11, and advances in recent days by pro-Assad forces had strengthened their control of the only route in.

“Today there is no way at all to bring anything into Aleppo,” Observatory Director Rami Abdulrahman said.

On the other hand, the U.S.-led coalition battling ISIS will look for chances to attack the hardline militant group in Syria from the south, potentially expanding U.S. efforts in that part of the country, U.S. Defense Secretary Ash Carter said on Wednesday.

“We will aggressively pursue opportunities to build pressure on ISIS in Syria from the south, complementing our existing and robust efforts,” Carter said, speaking to American troops at Fort Bragg, North Carolina.

“This of course will have the added benefits of helping the security of our Jordanian partners and further splitting the Syria theater of operation from the Iraqi theater of operation.”

Recently, most of the U.S.-led military coalition activity, including air strikes in support of the Syrian opposition, has focused on northern Syria.