DAMASCUS — Syria’s army and its allies have regained an important Aleppo district lost to rebels last month, state media and a war monitor said on Thursday, and were pressing an offensive south of the city to further squeeze the insurgents.

If sustained, the advance in Ramousah would reverse nearly all gains rebels made in a push last month, tighten a blockade over rebel-held eastern Aleppo and ease access for the army into government-held western districts through the city’s south.

A second line of attack, aimed at villages south of Aleppo and supported by what a pro-government fighter called “dusk to dawn” bombardment, is intended to isolate Telat al-Eis, a hill captured by rebels in May that commands fire over the region.

However, a rebel source said insurgents still held part of Ramousah and that though the army was mobilizing forces, the Jaish al-Fatah coalition of Islamist groups was still present at the southern Aleppo front.

In early August the rebel advance into southern Aleppo gave them control over the residential district of Ramousah, a complex of military colleges immediately to its west and the 1070 Apartment Blocks district west of that.

It opened a corridor into the rebel-held parts of Aleppo that are home to at least 250,000 people and had been under siege for weeks, while forcing the government to access its own areas in the city by a longer, more precarious route.

As international concern has mounted, the United Nations has renewed a call for weekly 48-hour humanitarian ceasefires to allow aid into the city, but efforts by Russia and the United States to agree terms for a truce are dragging.

On Thursday Russian Foreign Minister Sergei Lavrov and U.S. Secretary of State John Kerry discussed by phone potential cooperation to facilitate aid deliveries.

Syria’s five-year war has killed hundreds of thousands and displaced 11 million, half of Syria’s pre-war population, while drawing in world and regional powers, inspiring jihadist attacks across the world and sparking an international refugee crisis.