The UN is still unable to determine which side used chemical weapons in Syria’s conflict, the organization’s investigative committee has said. The statement came as reports of Syrian rebels being armed intensify and fears of more bloodshed mount.

Paulo Pinheiro, chairman of the UN commission’s inquiry into rights violations in Syria, refused to comment on evidence received from the US, UK, and France which, they claim, shows Syrian President Bashar Assad’s forces using chemical weapons.

"We are not able to say who has used chemical agents or chemical weapons and we are very worried about the chain of custody of the substances," Pinheiro told reporters after an informal meeting with UN Security Council ambassadors.

UN experts investigating the use of chemical weapons say they need to access Syria to determine where the alleged chemical weapons have been used. But Syria has thus far refused to grant them entry, citing concerns for their safety and doubts about their impartiality, as neither China nor Russia were allowed to participate.

Pinheiro's commission said in a report published this month that there were "reasonable grounds to believe that chemical agents have been used as weapons".

"Allegations have been received concerning the use of chemical weapons by both parties," said the commission, adding that "the majority concern their use by government forces."

Pinheiro believes that a "diplomatic surge" is needed to resolve the long-standing conflict, which has left more than 93,000 dead, according to UN figures.

However, just before foreign ministers from the "Friends of Syria" group met in Doha on Saturday, the main armed opposition group, the Free Syrian Army (FSA), told the AFP that it had new weapons that could beat President Bashar Assad's regime.

"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," FSA media spokesman Louay Muqdad said.

"We have begun distributing them on the front lines, they will be in the hands of professional officers and FSA fighters," he said.

These reports come after the US decided to arm the Syrian rebels, which reportedly sparked feuds among various rebel factions dominated by radical Islamist fighters.

President Barack Obama said on Friday that the US will leave about 700 combat-equipped troops in Jordan after a training exercise there, which would increase the number of US troops stationed there to almost 1,000. The US announced earlier that it will leave Patriot missiles and warplanes in the country.

The Qatari foreign minister supported and encouraged the idea of arming the Syrian opposition fighters during the foreign ministers’ meeting in Doha.

The EU lifted its arms embargo on Syria last month, and the UK and France spoke favorably about arming the rebels, though no decisions have been due to increasing concerns about the Islamist element within the Syrian rebel forces.

Risks of arming Syria

There are fears that a power struggle may be brewing in the rebels’ ranks, with fighters from the Al-Qaeda-linked Al-Nusra Front reportedly assassinating a large number of officers of the Free Syrian Army.

Russian President Vladimir Putin has warned the West against arming Syrian rebel forces, which he said included "terrorist" groups.

He reiterated that weapon supplies to the Syrian rebels would violate international law and threaten to further destabilize the war-torn state.

"Why supply weapons to militant forces in Syria when we are not sure of the composition of these groups?” he said Friday at the Economic Forum, adding that it remains unclear where these arms will end up.

"If the United States ... recognizes one of the key Syrian opposition organizations, al-Nusra, as terrorist ... how can one deliver arms to those opposition members? … Where will (those weapons) end up? What role will they play?" Putin said, arguing that a quick exit by President Bashar Assad would create a dangerous power vacuum.

Earlier on Friday, Pinheiro warned that sending more weapons into Syria would lead to more war crimes. "States that provide arms have responsibilities in terms of the eventual use of those arms to commit ... war crimes or crimes against humanity," Pinheiro said.

Putin also defended Russia’s contract to deliver advanced S-300 long-range air defense systems to Damascus, saying that Moscow maintains that all arms supplies to Syria are being carried out under a contract signed with the country several years ago.

"Russia, in the framework of existing international law, in open and transparent contracts, supplies weaponry to the current and the legitimate government of Syria," Putin said.

Putin has supported Pinheiro’s idea of a “diplomatic surge”, and insisted that an international peace conference is the right way to proceed to solve the Syrian conflict, referring to the earlier proposed peace conference in Geneva on June 25.

But the conference has been continually postponed. After the clash of G8 leaders with Russia over the nature of transitional government, the conference may be delayed until late August or early September.