The Republican senators John McCain and Lindsey Graham have criticised the deal struck by the US and Russia regarding the destruction of Syria's chemical weapons stockpile. In a statement released on Saturday, McCain and Graham said the deal would give the Syrian president, Bashar al-Assad, time "to delay and deceive" while the country's civil war continued.

The statement said: "It requires a willful suspension of disbelief to see this agreement as anything other than the start of a diplomatic blind alley, and the Obama administration is being led into it by Bashar Assad and [Russian president] Vladimir Putin."

The agreement, which is the result of three days of talks in Geneva between the US secretary of state, John Kerry, and Sergei Lavrov, the Russian foreign minister, was announced on Saturday morning. It requires Syria to provide a list of its chemical weapons within a week, to allow inspectors into the country by November and to help ensure the removal and destruction of all chemical weapons by the middle of 2014.

The US government says the Assad regime was responsible for a chemical weapons attack in Damascus last month that is believed to have killed more than 1,400 people. Assad. who has denied such culpability, offered this week to surrender his government's chemical weapons. On Saturday, the United Nations said it had received all documents necessary for Syria to join the Chemical Weapons Convention, and confirmed that Syria would come under the treaty starting on 14 October.

President Barack Obama welcomed the agreement achieved in Geneva, for providing "the opportunity for the elimination of Syrian chemical weapons in a transparent, expeditious, and verifiable manner, which could end the threat these weapons pose not only to the Syrian people but to the region and the world".

In their joint statement, however, McCain and Graham – who two weeks ago were invited to the White House, to discuss the administration's attempts to win Congressional support for military strikes in Syria – said: "What concerns us most is that our friends and enemies will take the same lessons from this agreement – they see it as an act of provocative weakness on America's part. We cannot imagine a worse signal to send to Iran as it continues its push for a nuclear weapon."

They added: "Assad will use the months and months afforded to him to delay and deceive the world using every trick in Saddam Hussein's playbook."

The statement concluded: "The only way this underlying conflict can be brought to a decent end is by significantly increasing our support to moderate opposition forces in Syria. We must strengthen their ability to degrade Assad's military advantage, change the momentum on the battlefield, and thereby create real conditions for a negotiated end to the conflict."