BEIRUT/THE UNITED NATIONS: Syrian regime forces and their allies bombarded rebels in southwestern Aleppo Tuesday, close to where rebels recently opened a corridor into the city’s opposition-held eastern sector, pro-Damascus media reported.

Hezbollah’s Al-Manar TV said government forces had advanced to cut off rebel progress into opposition-held areas of Aleppo. A rebel official denied any government advance in the area.

Fighting in Syria’s 5-year-old civil war has in recent months focused on Aleppo, Syria’s largest city before the conflict. Nearly 2 million people still live there.

Aleppo is split between the government-controlled west and rebel territory in eastern neighborhoods, which last month government forces put under siege by cutting the opposition supply route from the north.

Rebels effectively broke that siege in an assault on a major government military complex on Aleppo’s southwestern outskirts Saturday, opening a corridor linking the eastern sector with rebel territory.

At the same time, they cut the main supply route to government-held Aleppo, raising the prospect of rebels in turn besieging those areas.

This brought the total number of civilians in the city under “de facto fear of besiegement to over 2 million,” the U.N. said.

Government forces backed by intense aerial bombardment recaptured Tuesday some terrain and closed off the rebel corridor, pro-Damascus media outlets including Hezbollah’s Al-Manar TV reported.

A rebel official denied there had been a government gain. “There’s no advance, nothing,” said Abu al-Hassanein, a senior commander in Fatah Halab, the coalition of moderate rebel groups inside the city. “The situation is good. There’s a lot of bombing, but the brothers [fighters] are taking cover, until they start a new phase” in the battle, he said.

Ahmed Hamaher, a spokesman for the Nour al-din al-Zinki rebel group, said government forces had briefly overrun an area called Tallet al-Snoubrat, as reported by a pro-Damascus channel, but had been beaten back and the territory was recovered by rebels.

The Britain-based Syrian Observatory for Human Rights said government forces had not taken control of the southwestern areas that would cut the rebel corridor, but had temporarily blocked movement of insurgents with bombardments.

The Observatory reported that at least seven civilians were killed and 20 wounded Tuesday in regime airstrikes on Aleppo city. The group also said three people, including two children, were killed in rebel shelling on government-held areas in the city.

Meanwhile, Russia warned that the next round of peace talks should not be contingent on a halt to fighting in Aleppo after U.N. Syria envoy Staffan de Mistura told the U.N. Security Council he aims to reconvene negotiations in late August.

Speaking after a closed door meeting of the 15-member council, Russian U.N. Ambassador Vitaly Churkin told reporters: “The lower the level of violence the better it is for the talks ... but there must be no preconditions for the talks.”

Churkin called on countries with influence over the Syrian opposition to make sure they are prepared for future talks.

“They were coming to the talks without saying anything, they were just saying [Syrian President Bashar] ‘Assad must go’ and this is not a negotiating position,” he said.

Peace talks broke up last April after the opposition delegation quit, accusing the government of ignoring a cessation of hostilities brokered in February.U.S. Ambassador to the United Nations Samantha Power said the Syria peace talks urgently need to get back on track but “the environment for talks also has to be right.”

“On humanitarian access ... we’re in reverse gear. On the cessation of hostilities, we’re back to where we were before the cessation of hostilities, with the additional negative of Aleppo being besieged,” Power told reporters.

The United Nations has been calling for a weekly 48-hour pause in the fighting to access Aleppo. U.N. aid chief Stephen O’Brien, who also briefed the council, said talks were ongoing.

“I don’t see how we could have meaningful talks if there is not indeed the minimum conducive environment for that,” French Deputy Ambassador Alexis Lamek said.

Churkin said the United States and Russia were “very practically” discussing in Geneva how aid could be delivered to Aleppo and that Moscow supported a 48-hour pause in fighting, but that such a truce “does not apply to terrorists.”

The United Nations said Tuesday that 2 million people lack access to clean water in Aleppo, creating a risk of disease. It said technicians need access to repair electricity networks that drive water-pumping stations, which were heavily damaged in attacks last week.

Young children are especially vulnerable to diarrhea and other water-borne diseases from drinking dirty water, the U.N. Children’s Fund said. “In the eastern parts of Aleppo up to 300,000 people – over a third of them are children – are relying on water from wells which are potentially contaminated by fecal matter and unsafe to drink,” UNICEF spokesman Christophe Boulierac told a briefing.