Syrian rebels urged friendly world powers on Thursday to provide them with heavier weapons and to impose a no-fly zone over parts of the country they control to avert a humanitarian disaster.
On the ground, troops and rebels battled in several districts and suburbs of Damascus, and the army shelled insurgent positions with heavy artillery and mortars, the Syrian Observatory for Human Rights said.
Western and Arab powers from the so-called Friends of Syria group will meet in Doha on Saturday, and Free Syrian Army spokesman Louay Meqdad said "the regime could use Scud missiles with unconventional warheads to shell liberated areas. So we need a safe haven."
"It is necessary to establish secure areas and impose no-fly zones in the south or north," he told AFP in Dubai.
Calling for anti-tank and anti-aircraft weapons, he said that "if they do not provide us with arms to protect civilian areas, a humanitarian disaster will occur because regime troops are committing massacres in the areas they are recapturing".
Meqdad said "foreign militias, including (the Lebanese Shiite movement) Hezbollah and Abulfadhl al-Abbas brigades (made up mainly of Iraqi Shiites) do not respect any international conventions".
Foreign ministers from Britain, Egypt, France, Germany, Italy, Jordan, Qatar, Saudi Arabia, Turkey, the United Arab Emirates and the United States are to discuss aid for the rebels, including military help, a French diplomat said on Wednesday.
Western powers have so far refused to arm rebels fighting Syrian President Bashar al-Assad's troops -- backed by Shiite militias from neighbouring countries -- out of fear they could fall into the hands of radical Islamists.
But Meqdad said "we are committed to ensuring that these weapons do not fall into the hands of unorganised or extremist groups".
FSA chief of staff General Selim Idriss is seen as a reliable partner by the West, who mainly voice fears of groups such as Al-Nusra Front, whose aim is to establish an Islamic state in Syria.
Meqdad said the regime has been amassing troops in preparation for an offensive on rebel-held areas on the outskirts of Damascus and second city Aleppo.
The expected campaign comes after Assad forces regained control of the strategic town of Qusayr, on the border with Lebanon, with Hezbollah help.
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On Thursday, Lebanese President Michel Sleiman urged Hezbollah to end its participation in the war "because this intervention leads to tensions in Lebanon".
The opposition has said Hezbollah forces are now deploying at other key sites in the country, including in the north.
"If they (Hezbollah) participate in the battle in Aleppo and there are more deaths in the ranks of the party it will raise tensions further. Qusayr must be the end, and they must return to Lebanon," Sleiman said.
In Moscow, meanwhile, Russian Foreign Minister Sergei Lavrov said the West was dragging its feet on agreeing to a date for a peace conference because "they are not at all sure that they will be able to sell the opposition".
Speaking of this week's G8 summit in Northern Ireland, Lavrov said Russia pushed for a concrete time frame to be spelled out but its Western partners refused to do so.
The opposition has long insisted that Assad's departure is a precondition for any settlement, and said it "reserves the right to use all means at its disposal" to bring him down, "chiefly military action".
The army, in some instances backed by Hezbollah, was seeking to retake rebel positions in suburbs south of the capital, and to sever supply lines to others inside the capital, the Britain-based Observatory said.
It said the Jubar and Barzeh districts were bombarded, and a Syrian National Coalition statement said the two areas were at risk "after six months of continuous siege, military checkpoints and the recent support from Hezbollah."
"The lives of 40,000 civilians are suffering with a lack of food and medical supplies," the coalition said.
The Observatory also reported bombardments in the central provinces of Homs and Hama, Daraa in the south and Deir Ezzor in the east.
At least 93,000 people have died in more than two years of violence in Syria.
Meanwhile, US Secretary of State John Kerry said Washington was doubling its aid to the UN refugee organisation this year to some $890 million (674 million euros).
UNHCR chief Antonio Guterres said: "In the first six months there will be more refugees coming out of Syria than all the refugees that came from all parts of the world into neighbouring countries in the whole of 2012."