Syrian troops pushed into a rebel-held town near the Lebanese border on Sunday, fighting house-to-house and bombing from the air as President Bashar Assad tried to strengthen his grip on a strategic strip of land running from the capital to the Mediterranean coast.

With the regime scoring gains on the battlefield, the U.S. and Russia could face an even tougher task persuading Assad and his opponents to attend talks on ending Syria’s 26-month-old conflict. Washington and Moscow hope to start talks with an international conference as early as next month, though no date has been set.

Government forces launched the offensive on the town of Qusair just hours after Assad said in a newspaper interview that he’ll stay in his job until elections — effectively rejecting an opposition demand that any talks on a political transition lead to his ouster.

Even though the regime and the main opposition group have not yet committed to attending the conference, U.N. Secretary General Ban Ki-moon said Sunday that he is hopeful it can take place “very soon,” possibly in early June. In addition to the U.S. and Russia, he said he has spoken with Britain, France, China and other key parties.

Previous diplomatic initiatives have failed, in part because of divisions within the international community and because the regime and the armed opposition believed they could achieve more on the battlefield than in talks. Russia and the U.S. have backed opposite sides in Syria.

Still, neither regime forces nor rebel fighters have been able to create significant momentum since the uprising against Assad erupted in March 2011 and last year escalated into a full-fledged civil war.

The rebels control large rural areas in the north and east of the country, while Assad has successfully defended his hold on the capital, Damascus, the coastal area and parts of Aleppo, Syria’s largest city.

Before Sunday’s offensive, Qusair had been ringed by regime troops and fighters from the Lebanese militia Hezbollah, an Assad ally, for several weeks.

Qusair lies along a land corridor between Damascus and the Mediterranean coast, the heartland of Assad’s Alawite sect, an offshoot of Shiite Islam. Many rebel fighters are Sunni Muslims and Qusair, overwhelmingly Sunni, had served as a conduit for shipments of weapons and supplies smuggled from Lebanon to the rebels.

Hadi Abdullah, a Qusair activist reached by Skype, said regime troops and Hezbollah fighters began shelling the town late Saturday, followed by airstrikes early Sunday that sent residents taking cover in basements. The Britain-based Syrian Observatory for Human Rights, an activist group, said warplanes resumed bombing raids later Sunday.

The Observatory said 52 people were killed in Qusair, including 48 fighters, three women and a male civilian.

Abdullah said the air raids destroyed at least 17 houses. A field hospital was damaged last week, leaving the town with only one medical center which was unable to handle the influx of some 400 wounded Sunday, he said.

The main political opposition group, the Syrian National Coalition, said some 40,000 civilians are in Qusair and expressed concern for their safety. It urged the international community to step in to protect the lives of the civilians and called on the U.N. Security Council to denounce Hezbollah’s involvement in the attack.

Also on Sunday, Israeli Prime Minister Benjamin Netanyahu warned that he is ready to act if Syria attempts to ship advanced Iranian weapons to Hezbollah, saying that “we are prepared for every scenario.” Earlier this month, Israel struck twice near Damascus, to intercept purported shipments to Hezbollah.