Obama gives Putin his best death stare: Tense moment the world's two most powerful men squared up at the G20 summit in China

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Barack Obama and Vladimir Putin have met for 'pull-aside' meetings at the G20 summit in China but failed to agree on a solution to the Syrian civil war.

Washington and Moscow support opposing sides in the bloody five-year conflict, which has left 300,000 people dead and forced millions to flee. 

The two leaders discussed Syria at closed multilateral meetings but could not reach a deal to ease fighting in the war-torn region.

But in their final face-to-face meeting before Obama leaves office in January next year, they agreed to keep up negotiations over a cease-fire agreement.

Speaking today Obama said the pair had a 'candid, blunt, business like meeting'.

It comes as Syrian government troops - backed by Russia - resumed their siege of the city of Aleppo.

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Tense: Vladimir Putin and Barack Obama failed to agree on a solution to the Syrian civil war

Stand off: Obama expressed skepticism that Russia would keep to its side of the agreement

A deal to provide aid to Aleppo's ravaged civilians and at least partially stop Russian and Syrian bombardments had looked likely on Sunday, before talks collapsed.  

Secretary of State John Kerry and Russian foreign minister Sergey Lavrov had been trying to broker a deal for weeks that would curb the violence between Assad's government forces and rebel forces backed by the US.

The agreement hinged on the two sides agreeing to closer militarily coordination against extremist groups operating in Syria. 

But Obama expressed skepticism that Russia would hold to its agreement and talks were overtaken by developments on the ground. 

Unofficial meeting: They have agreed to keep up negotiations over a cease-fire agreement

Summit: Putin also met Secretary of State John Kerry on the sidelines of the G20

State media said Syrian government troops had taken an area south of Aleppo, severing the last opposition-held route into its eastern neighbourhoods.

He said today: 'We are back in a situation where Assad is bombing without impunity and strengthening Nusra's position to recruit people for terrorism and that's a dangerous dynamic. 

'We want to have productive discussions that would allow us both to focus on our common enemies like ISIS but there are gaps of trust and we haven't yet closed the gap. 

'We will keep working at it over the next several days. The faster we can provide relief the better off we will be and we can have a serious conversation about this involving all the parties who are involved in Syria.'  

Turkish President Tayyip Erdogan said he had urged world powers at a G20 meeting to set up a 'safe zone' in Syria where there would be no fighting and which could help stem migrant flows from the Arab nation.

Claims: Obama later described the meeting as 'blunt' during a press conference 

Leader: Putin was meeting Obama for the last time before the latter leaves office

Speaking in China, Erdogan said he had repeated a proposal for a 'no-fly zone' in Syria during his talks with Putin and Obama.  

Away from Syria, he also discussed Ukraine and said until the Minsk Agreement was implemented the US would not pull down their sanctions with Russia. 

He said it was important for both sides over the next few weeks to seize the opportunity to finalize the agreement. 

The president said he expressed concerns about cyber security issues with Mr Putin, but would not detail the discussions. 

The meeting came as it emerged US intelligence officials are probing claims that Russia could be trying to influence the result of the American presidential election.

Director of national intelligence James R. Clapper Jr is spearheading the investigation, it was reported today.

The FBI has already alerted local authorities to cyber threats targeting the election - while Republican candidate Donald Trump previously warned the vote would be 'rigged'.

Syrian soldiers give the victory sign on September 4, 2016 on the outskirts of the city of Aleppo 

Washington has repeatedly said that Assad must step down in order for a lasting peace deal.

Turning up the heat in recent weeks, the White House has gone as far as to suggest Moscow is complicit in war crimes.

'You have the Assad regime which has been killing its own citizens with impunity, supported by the Russians and the Iranians,' Obama said on Sunday.  

He added: 'Our conversations with the Russians are key because if it were not for the Russians, then Assad and the regime would not be able to sustain its offensive.

'But it is worth trying. To the extent that there are children and women and innocent civilians who can get food and medical supplies and get some relief from the constant terror of bombings, that's worth the effort.' 

The failure to reach a deal is likely to heap pressure on Obama over his handling of the war in Syria.

Obama came to office vowing not to repeat the mistakes of his predecessor George Bush, who launched disastrous wars in Iraq and Afghanistan.

But as he prepares to leave office, critics claim Obama's failure to intervene in Syria has had similarly bloody results, allowing the conflict to fester for years.