WASHINGTON - The White House on Wednesday denounced the Syrian government's recapture of the strategic central city of al-Qussair after a two-week-long offensive against the rebels, repeating a call for Hezbollah and Iran to withdraw their fighters from Syria.

"The United States condemns in the strongest possible terms the al-Assad regime's assault on al-Qussair, which has killed untold numbers of civilians and is causing tremendous humanitarian suffering," spokesman Jay Carney said in a statement, calling for "safe access" to evacuate the wounded and provide medical supplies and treatment.

"Hezbollah and Iran should immediately withdraw their fighters from Syria," Carney added, accusing the two of aiding the Syrian government in its battle for al-Qussair.

The Syrian troops early Wednesday regained full control of al- Qussair, a city near the border with Lebanon. The operation aimed at cutting the rebels' main supply line in the central region of the country.

Carney also condemned the reported raid on Lebanon's northeastern town of Arsal on Wednesday by the Syrian air force, calling it "blatant violations of Lebanon's sovereignty and a deliberate threat to Lebanese stability."

Meanwhile, a new peace conference will not take place in June as envisaged by the US and Russia, the United Nations-Arab League joint special representative for Syria Lakhdar Brahimi said on Wednesday.

"There is still a lot of work to do to bring a conference about. For this reason, we have come to a conclusion that it will not be possible to hold this conference in June," Brahimi told reporters after meeting with senior officials from the US and Russia.

He expressed hope that the conference will be held in July to explore ways to stop the conflict in Syria, which started in March 2011 and has killed more than 80,000 people.

Washington and its allies are aiding the opposition in its efforts to topple President Bashar al-Assad.