The International Committee of the Red Cross said on Monday it was still seeking a formal Syrian response to its request for urgent access to the besieged town of Qusayr after a minister said aid efforts should wait until the fighting was over.
Humanitarian groups say as many as 1,500 wounded people may be trapped in Qusayr by fighting between rebels and President Bashar al-Assad's forces, who are backed by fighters from Lebanon's militant Shi'ite group Hezbollah.
At least 80,000 people have lost their lives in the two-year uprising against Assad, whose Alawite minority is an offshoot of Shi'ite Islam.
"We remain alarmed about the current situation in Qusayr where food, water and medical supplies are reported to be very scarce," ICRC spokesman Alexis Heeb said.
"We want access. We have requested this access," he said. "When we get the green light we also have to make sure the security conditions are acceptable to send the assistance."
He was speaking a day after Syria's Foreign Minister Walid al-Moualem told U.N. Secretary General Ban Ki-moon that Syria would grant the Red Cross and the Syrian Arab Red Crescent access to Qusayr "as soon as military operations are over".
The assault on Qusayr began two weeks ago. An ultimatum from the army and Hezbollah to evacuate civilians was ignored by fighters in the town who said they did not trust authorities to allow safe passage.
Assad's soldiers and Hezbollah have since all but surrounded the strategic border town, used by rebels as a transit point for weapons and fighters smuggled into Syria, and appear to hold much of the town itself.
But rebels say they have brought fighters from the northern province of Aleppo and other regions of Syria, slipping them through the army's lines to reinforce Qusayr.
Assad's efforts to recapture Qusayr follow a series of counter-offensives in southern Syria and east of Damascus which have consolidated his hold over central Syria ahead of planned peace talks promoted by the United States and Russia.
The 47-year-old president says he supports negotiations in principle, but last week dampened prospects for a breakthrough by saying that any change to his powers must be approved in a referendum, undermining chances for political transition.
Despite Washington and Moscow's joint push for talks, the two powers are still divided over Syria's civil war, which has driven 1.5 million refugees out of Syria and escalated regional sectarian tensions. The United States has provided non-lethal aid to rebels, while Russia continues to supply Damascus with arms.
Russian Deputy Foreign Minister Sergei Ryabkov said on Monday the United States was not doing enough to get the opposition to participate in the talks.
"In our view, the United States is definitely not working hard enough in terms of putting influence on Syrian opposition groups so that (they) will come to the international conference," Russia's RIA quoted Ryabkov as saying.
He said the United States "should not allow the opposition to try to issue ultimatums and impose preconditions. The main such condition ... is the demand for Syrian President Bashar al-Assad's exit."
The European Union, which last week let lapse a ban on weapons supplies to Syrian rebels under pressure from France and Britain, said it was deeply concerned over the fighting in Qusayr and urged both sides to ensure safe access for aid.
EU foreign policy chief Catherine Ashton's office said she was appalled at the level of violence in and around the city, adding that there would be "no impunity for the perpetrators".
The fighting in Syria has raised tensions in neighbouring Lebanon, which suffered its own 1975-1990 civil war and whose society reflects the same sectarian divisions as its larger and once-dominant neighbour.
Overnight fighting in the northern city of Tripoli left four people dead and 27 wounded, security and medical sources said.
Most people in the mainly Sunni Muslim city of Tripoli support the Syrian uprising, but a small community of pro-Assad Alawites - from the same minority sect as the president - live in a district overlooking the centre of the city.
To the south, in the Mediterranean city of Sidon, a Sunni Muslim cleric survived an assassination attempt when gunmen fired on him as he walked to his mosque for dawn prayers, security sources said. The gunmen missed their target and fled when his guards returned fire.