Russia-US tensions: Cabinet gives May the go-ahead for Syria strike 'to deter further use of chemical weapons by the Assad regime'

Russian ships have left the Tartus naval base in Syria, a Russian MP has said, according to the Interfax news agency.

Vladimir Shamanov, who chairs the Russian defence committee of the lower house of parliament, said the vessels had left the Mediterranean base for their own safety.

"... this is normal practice" when there are threats of an attack he said.

Russia has warned the US and its allies against assuming the role of a "global policeman" in response to what it describes as fake claims of chemical weapons use in Syria. 

A spokeswoman for the Russian foreign ministry, Maria Zakharova, said Western leaders have no authority to be "investigators, prosecutors and executioners." 

Ms Zakharova described the chemical weapons allegations as fake, but said the international chemical weapons watchdog should investigate them. She said Russia would ensure the monitors' security. 

She went on to call for de-escalating the situation, urging the West to carefully weigh the consequences before taking any action. 

Amber Rudd, the home secretary, has arrived at No 10 for Theresa May's emergency cabinet meeting.

The defence secretary, Gavin Williamson, and culture secretary, Matt Hancock, have also arrived at No 10.

Caroline Lucas, the leader of the Green Party, argues MPs must be given a vote on any decision to intervene in Syria. 

The United States is committed to ending the Syrian civil war through the Geneva process, the US defence secretary, James Mattis, has said.

Mr Mattis told congress Russia was complicit in Syria's retention of chemical weapons.

He said he would notify congress leaders before any strike in Syria. 

As the US weighs military action, Mr Mattis said the country was looking to avoid stoking an escalating situation in Syria that gets "out of control."

"I believe there was a chemical attack," he said. 

The head of the intelligence agency GCHQ has said the Salisbury nerve agent attack last month shows how “reckless” Russia is prepared to be, Ashley Cowburn writes.

In his first speech since taking the job at the secretive department last year Jeremy Fleming — formerly a senior MI5 office — took aim at Moscow, describing recent actions as “particularly stark and shocking”.

Speaking at cyber conference on Thursday, he said: It demonstrates how reckless Russia is prepared to be. How little the Kremlin cares for the international rules-based order. How comfortable they are at putting ordinary lives at risk.

"The robust response from the UK and from the international community shows the Kremlin that illegal acts have consequences.

"And it looks like our expertise on Russia will be in increasing demand."

US Defence Secretary Jim Mattis has told Congress that he believes there was a chemical attack in Syria and said United States wants inspectors on the ground to collect evidence as soon as possible.

He warned collecting evidence will become more difficult as time passes.

"I believe there was a chemical attack and we are looking for the actual evidence," Mr Mattis told a hearing of the House Armed Services Committee.

He added one of his major concerns about any US military strike was preventing an "out-of-control" escalation in the Syrian civil war, in which Russia, Iran, Turkey and others have taken sides.

Mr Mattis also accused Russia of being complicit in Syria's retention of chemical weapons, despite a 2013 deal requiring Syria to abandon them that Moscow helped broker.

Nato is calling on Russia and Iran to ensure international observers and medical staff are allowed in and around the area of the suspected chemical attack in Syria. 

Secretary general Jens Stoltenberg earlier urged Syrian president Bashar Assad to allow "full and unimpeded access to international medical assistance and international monitoring".

Speaking to reporters this afternoon, he said it was also up to the regime's supporters Iran and Russia to "make that possible".

The Russian military says Syrian government forces are in full control of Douma, where a suspected gas attack last week killed more than 40 people.

Mr Stoltenberg said that consultations were ongoing among Nato allies on how to respond to the attack and said "it is important that those responsible are held accountable."