Russian President Vladimir Putin on Monday told British Prime Minister David Cameron that there was no evidence yet that the Syrian regime had used chemical weapons against rebels, Cameron's office said.
During a telephone call between the two leaders, Putin said that "they did not have evidence of whether a chemical weapons attack had taken place or who was responsible," according to a Downing Street spokesman.
Cameron insisted that there was "little doubt" Bashar al-Assad's regime had carried out a chemical attack, according to a readout of the telephone conversation.
The British leader doubted that the rebels had the capability to carry out such an attack and pointed out that the regime had launched a heavy offensive in the area in the days before and after the incident.
"The regime had also prevented UN access in the immediate aftermath, suggesting they had something to hide," he told Putin.
However, the pair did both repeat their commitment to an agreement reached by G8 leaders in June, which resolved that no-one should use chemical weapons and any use would merit a serious response from the international community.
Russian news agency Ria-Novosti, quoting the Kremlin press office, said that the conversation had "focused mainly on the situation in Syria against the backdrop of media reports on the possible use of chemical weapons near Damascus".
Western nations have upped the rhetoric since reports that chemical weapons were used last week and Britain maintains there is evidence suggesting the regime was responsible.
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Cameron already spoke with US President Barack Obama over the weekend to formulate a response to the escalation in the 29-month-old Syrian conflict.
Foreign Secretary William Hague said an international response was possible without the formal backing of the United Nations.
Russia, also a veto-wielding member of the UN Security Council, has repeatedly warned Washington and its allies against military action in Syria.
Syrian President Assad has denied using chemical weapons and warned Monday that any Western strikes against his regime would be doomed to failure.
Moscow, which has backed him throughout the crisis, urged Washington not to preempt the results of the UN inspection and warned that any military action would be a "tragic mistake".
Cameron's office said the British government will decide on Tuesday whether to recall lawmakers to debate the situation sooner than September 2, when the House is currently due to return.
The prime minister has cut short his holiday to deal with the crisis, and will chair his National Security Council (NSC) on Wednesday.
The NSC, which meets weekly, comprises 10 high-ranking government ministers. Other cabinet ministers plus defence and intelligence chiefs attend when required.