China has said that resolving the Syrian crisis is not possible without the participation of Saudi Arabia and Iran at a key peace conference slated for June.

Russian agencies reported Chinese foreign ministry spokesperson Hong Lei as saying on Tuesday that his country supports efforts to resolve the Syrian conflict politically.

"We believe that a settlement is not possible without the participation of influential countries in the region, particularly of those in the forefront which have a direct effect on the Syrian situation," he added. 

Iran has voiced an interest in joining the conference, citing its right to participate as an influential party and a member of the international community, AFP reported.

Moscow, a longtime ally of Iran, requested that the country be included in the talks.

The conference, brokered by US and Russia which support opposite parties in the conflict, will aim to bring Bashar al-Assad's regime and the Syrian opposition to the same negotiating table. 

Al-Assad has already put forth names for the delegation he hopes to send to the negotiations. 

The Syrian opposition, which is yet to confirm its participation after meeting in Istanbul on Thursday, has been encouraged by the international community to join the talks.

The bottom line for the opposition's participation, however, is the departure of Al-Assad, a demand that Al-Assad has categorically struck down time and again.

"To resign would be to flee," he told an Argentinean newspaper earlier this week.