Syria's rebels have received new types of weapons that could "change the course of the battle," a rebel spokesman said on Friday, as troops tried to oust opposition fighters from a Damascus district.

The announcement came a day before a meeting in Qatar of the "Friends of Syria" group of nations that back the uprising against President Bashar al-Assad.

"We've received quantities of new types of weapons, including some that we asked for and that we believe will change the course of the battle on the ground," Free Syrian Army spokesman Louay Muqdad told AFP.

"We have begun distributing them on the front lines; they will be in the hands of professional officers and FSA fighters," added Muqdad, a media and political coordinator for the FSA.

He said the Friends of Syria meeting was expected to officially announce on Saturday its members would arm the rebels.

Muqdad declined to specify what weapons had been received or when they had arrived, but added that a new shipment was expected in the coming days.

He said rebels had asked for "deterrent weapons," meaning "anti-aircraft weapons, anti-tank weapons, as well as ammunition."

The apparent influx of weapons comes after the United States said it would provide rebel forces with "military support," although it has declined to outline what that might entail.

"The weapons will be used for one objective, which is to fight the regime of Bashar al-Assad," Muqdad insisted.

"They will be collected after the fall of the regime, we have made this commitment to the friends and brotherly countries" that supplied them, he said.

On Thursday, Muqdad said rebels needed short-range ground-to-air missiles, surface-to-air missiles known as MANPADs anti-tank missiles, mortars and ammunition.

The Friends of Syria talks in Doha will be attended by ministers from Britain, Egypt, France, Germany, Italy, Jordan, Qatar, Saudi Arabia, Turkey, the United Arab Emirates and the United States.

They are expected to discuss military help and other aid for rebels as government forces press their campaign against the insurgents.

Muqdad said the opposition was expecting "a clear and official announcement by the countries participating (in Doha) on the arming of the FSA".

"That's what we are hoping for; that's what we are waiting for."

Senior opposition figure Burhan Ghalioun confirmed that the FSA had recently received "sophisticated weapons" including "an anti-aircraft defence system".

Another opposition source, speaking on condition of anonymity, said the system was "Russian-made" but declined to say who had supplied it.

Russian President Vladimir Putin on Friday warned the West against arming the opposition, saying some 600 Russians and Europeans are fighting within the rebel ranks.

"So why deliver arms to illegal armed groups in Syria, if we do not have a clear understanding of who they are comprised of? Where would these arms end up?" he asked.

US Secretary of State John Kerry left for Qatar on Friday, with a US official describing the gathering as important for "energising" the opposition Syrian National Coalition.

On the ground, troops shelled the Damascus neighbourhood of Qabun, as their bid to drive rebels from the district entered a third day, the Syrian Observatory for Human Rights said.

"Regime troops renewed shelling this morning of the Qabun neighbourhood and fierce clashes were underway between soldiers and rebels on the outskirts of the area," it said.

"Regime forces are hitting the area with mortar rounds, tanks and heavy artillery."

Meanwhile, state television reported that the army had killed "several terrorists (rebels) around the Aleppo central prison, and destroyed anti-aircraft guns as well as weapons caches".

State media denied there were medical shortages at the prison, where the Observatory has said more than 100 people have died since April, some for lack of medical treatment.

Colonel Abdel Jabbar al-Okaidi, the Aleppo rebel council chief, said in a video posted online on Friday that he was standing down from his position as FSA chief of staff but would remain local commander.

In Lebanon, where the Syrian conflict has inflamed tensions between Sunni and Shiite Muslims, a security source confirmed that a rocket fired from north of Beirut hit near the capital overnight.

The rocket caused no injuries and it was unclear what it was targeting.

Violence from Syria has spilled over in recent months, with rockets fired from across the border hitting northern and eastern Lebanon.

Meanwhile, the head of a UN human rights investigation on Syria said it was still impossible to tell for sure who has used chemical weapons in the conflict.

Paulo Pinheiro said he would not comment on evidence sent by the United States, Britain and France to UN experts which they say shows Assad's forces have used chemical arms.