Astana (Kazakhstan) (AFP) - Russia has given rebels a draft version of a new constitution for Syria drawn up by Moscow to speed up political negotiations to end the conflict, the Kremlin's envoy said Tuesday.

"We have handed the Syrian armed opposition a draft constitution of Syria prepared by Russian specialists for them to study," Russia's envoy for Syria, Alexander Lavrentiev, told reporters. "We did this exclusively to accelerate the process" to end the war.

The rebels, however, told AFP they had refused to discuss the draft constitution with Moscow.

"The Russians put the draft on the table and we didn't even pick it up," a source from the rebel delegation in Astana told AFP. "We told them we refuse to discuss this."

Two days of indirect talks between rebels and regime representatives in the capital of Kazakhstan ended on Tuesday with no sign of a breakthrough towards a broader political settlement to end the war.

Russia -- the driving force behind the meeting -- has become the major powerbroker in Syria after changing the tide on the ground with its military support for leader Bashar al-Assad.

After the talks, sponsors Russia, Iran and Turkey said they had agreed to bolster Syria's frail ceasefire by implementing a "trilateral mechanism".

Coming up with a new constitution for post-conflict Syria is seen as a major hurdle for any talks to end the bloodshed that has cost more than 310,000 lives since protests against Assad erupted into conflict in 2011.

Russia and the United State had pushed for the two sides to come up with a new constitution for the war-torn country by August 2016 during previous unsuccessful talks.

A constitution adopted in 2012 left President Bashar al-Assad with sweeping powers, including the right to name the premier and government and, in some cases, veto legislation.