UN leader Ban Ki-moon said Friday he shares international doubts that Syria's President Bashar al-Assad will respect an international deal on his country's chemical weapons.

A Russian plan to put Syria's chemical weapons under international control and an application by Damascus to join the 1993 Chemical Weapons Convention have eased fears of a US military strike.

"President Assad has seemingly positively responded" to Russia-US talks on ending the crisis, in part by applying to join the convention, Ban told the France 24 television news channel in an interview.

"That is positive, but at the same time I sense in the international community some sense of skepticism."

"Yes, I also share" the doubts, he added.

"It is important for Syrian authorities to make sincere and faithful implementation of what they have said to prove that they are, (and) President Assad is, sincere," the UN secretary general added.

The United States and its allies have expressed doubts about Assad's intentions and called for guarantees that international action be taken if the Syrian government fails to hold up its end of the deal.

Ban gave the interview after saying he believed that a UN expert report would next week give "overwhelming" confirmation that chemical weapons have been used in Syria.

UN inspectors are expected to give their report on a suspected sarin attack near Damascus on August 21 to Ban on Monday.

The UN leader also said that Assad has "committed many crimes against humanity."

In the France 24 interview, Ban reaffirmed that "horrible crimes" have been committed in Syria and that there has to be accountability.

But he also said that only a political solution could end the 30-month old conflict in which more than 100,000 people have been killed.

Ban said a peace conference in Geneva could be held in October if the chemical weapons crisis is ended and international negotiators can overcome divisions in the Syrian opposition.

"We are targeting to do it some time in October but we will have to work very hard," Ban said.