Ankara - Russia and Turkey have agreed to support an independent investigation into the use of chemical weapons in northern Syria.

Mr Erdogan's office said he and Russian President Vladimir Putin had agreed to back a probe by the Organisation for the Russia has agreed to support an independent investigation into the use of chemical weapons in northern Syria, Turkish President Recep Tayyip Erdogan has said.

Mr Erdogan's office said he and Russian President Vladimir Putin had agreed to back a probe by the Organisation for the Prohibition of Chemical Weapons (OPCW).

A spokesman said the two leaders held a telephone conversation on Thursday, during which the Turkish leader stressed that the use of chemical weapons 'is the greatest crime against humanity'.

A statement said: 'The two leaders agreed that the attack in question be investigated by the OPCW, which is an independent organisation whose legitimacy is recognised.'

Mr Erdogan and Mr Putin also discussed peace efforts for Syria and their joint efforts to extend a ceasefire agreement to the whole of the country.

Syria strongly denied it was behind the April 4 chemical attack on Khan Sheikhoun, which killed 87 people.

Russia demands a UN impartial inveistigation, while UN sources assured that a team is already on the ground selecting samples and they expect to informed their findings within 3 weeks.