Syria's air force has bombarded Qusayr, two weeks into a Hezbollah-backed assault, as a car bomb in Damascus killed nine members of the security forces.
The regime responded to a Red Cross appeal to let them help civilians trapped in Qusayr by saying they would only be admitted once its forces had defeated rebels there.
At the United Nations, diplomats said Russia blocked a draft Security Council declaration expressing "grave concern" about the situation in the strategic town near the border with Lebanon.
France meanwhile said that the Geneva peace conference on ending the bloodshed could be delayed.
The car bomb in Damascus added to an estimated 94,000 lives lost in the conflict which broke out more than two years ago.
The Syrian Observatory for Human Rights said the suicide attack appeared to have been carried out by the jihadist Al-Nusra Front, although there was no confirmation.
"At least nine regime forces were killed in the explosion of a car bomb near a police station in the Jubar neighbourhood," Observatory director Rami Abdel Rahman told AFP.
State news agency SANA reported "10 citizens were wounded when a car driven by a terrorist exploded in Jubar", but gave no information on deaths.
In the central province of Homs, regime warplanes carried out multiple raids yesterday against the northern part of Qusayr and the area between the town and Dabaa, said the Observatory.
A day earlier, international aid groups had called for the evacuation of civilians trapped in the town, where regime forces backed by fighters of the Lebanese Shiite movement Hezbollah launched an all-out offencive on May 19.
But Syria's Foreign Minister Walid Muallem told UN chief Ban Ki-moon in a telephone call that the Red Cross would not be allowed to enter until the assault is over.
"Syrian authorities will allow the Red Cross in cooperation with the Syrian Red Crescent access to the area immediately after the end of military operations," SANA quoted him as saying.
The Observatory said the regime has continued to bolster its forces in Qusayr, key to the regime and the rebels alike as it links Damascus to the coast, and is near the Lebanese border, providing a conduit for weapons and fighters.
On Saturday, Ban and international aid groups expressed concern about civilians trapped in Qusayr, and for between 1,000-1,500 injured residents still in the town of 25,000 people.
