Turkey has a duty to defeat the so-called Islamic State (IS) in neighbouring Syria, President Recep Tayyip Erdogan has said.

He called it a "binding duty", to ensure the militants were "unable to carry out actions inside our country".

Turkey's military said its warplanes killed 20 IS fighters during air raids over Syria on Saturday.

A 10-day truce is due to start in Syria on Monday, followed by co-ordinated air strikes against jihadist militants.

The cessation of hostilities was agreed on Friday between the US and Russia, which is an ally of Syria's President Bashar al-Assad.

Mr Erdogan said in a statement that the current Turkish military operation in Syria, known as Operation Euphrates, was just a "first step" in the fight against IS, which he calls Daesh.

"It is our duty to our people to finish off Daesh in Syria, and to bring them to a level where they can't carry out attacks in our country," he said.

In the same statement, he said Turkey was also determined to defeat the outlawed Kurdish Workers' Party (PKK) and the Feto group of US-based cleric Fethullah Gulen.

Mr Erdogan has accused Mr Gulen of masterminding a failed coup attempt in July.

"We are determined to wipe out the PKK trouble from Turkey together with our security forces. Just like Feto, the PKK stands no change against our sagacious people and the power of our state."