The Saudi foreign minister has expressed doubt about the seriousness of Iran and Russia in finding a political solution to the crisis in Syria.

"If they're serious, we will know, and if they're not serious, we will also know and stop wasting time with them," Adel al-Jubeir said at a press conference with visiting British Foreign Secretary Philip Hammond in the Saudi capital, Riyadh, on Wednesday.

He made the comments ahead of an upcoming two-day conference in Vienna, Austria, beginning on Thursday, with the aim of exploring ways to end over four years of deadly violence in Syria.

The talks would "test the intentions of the Syrians and the Russians," Jubeir added.

Hammond, for his part, said the conference provides an opportunity to find out if it is possible to "bridge the gap" between Iran and Russia on one side, and other countries on the other over the role of Syrian President Bashar al-Assad in the future of the crisis-hit state.

Moscow and Tehran say Assad should be able to stand for re-election since it is for the Syrian people to decide on his future, while the West and its regional allies insist Assad should go.

Jubeir, meanwhile, called for the departure of President Assad, saying, “There has to be certainty that Bashar al-Assad will leave.”

Earlier on Wednesday, Tehran said Iranian Foreign Minister Mohammad Javad Zarif would be present in Vienna at the head of a high-ranking political delegation for talks on the situation in Syria. Zarif’s counterparts from Russia, the United States, Turkey and Saudi Arabia would also join the meetings.

Two conferences were previously held in an attempt to resolve the crisis in the Swiss city of Geneva, one in 2012 and the other in 2014. However, both events ended in failure amid the absence of Iran, an important regional player.

Iran was not invited to the first one, and while the country primarily received an invitation to take part in the second Geneva conference, UN Secretary General Ban Ki-moon later rescinded the invitation under pressure from the United States, Saudi Arabia, and the foreign-backed Syrian opposition.

The Islamic Republic has on numerous occasions insisted that diplomacy is the only solution to the chaotic situation plaguing Syria.

Riyadh and a number of its regional allies have been accused of supporting Takfiri terrorist groups operating mostly in Syria, Iraq and Libya. Most of the militants fighting Damascus are known to follow the Wahhabi ideology, an extremist mentality that is officially preached in Saudi Arabia.