Chinese Vice Minister of Foreign Affairs Li Baodong (2nd L) and Iranian Foreign Minister Mohammad Javad Zarif (2nd R) wait with others before a meeting with 17 nations, the European Union and United Nations at the Hotel Imperial in Vienna, October 30, 2015. Reuters DUBAI (Reuters) - Iran said on Monday it would pull out of Syria peace talks if it found them unconstructive, citing the "negative role" of its main regional adversary Saudi Arabia, according to state Iranian media.

World and regional powers including Iran and Saudi Arabia met in Vienna on Friday to discuss a political solution to Syria's civil war but failed, as expected, to reach a consensus on the future of President Bashar al-Assad.

Iran backs Assad in the war while Saudi Arabia supports rebels seeking to oust him.

It was the first time Tehran and Riyadh were at the same table to tackle a war that has evolved into a wider proxy struggle for regional dominance between Russia and Iran on Assad's side and Turkey, U.S.-allied Gulf Arab states and Western powers who support rebels to various degrees.

"In the first round of talks, some countries, especially Saudi Arabia, played a negative andunconstructive role … Iran will not participate if the talks are not fruitful," ISNA cited deputy Foreign Minister Hossein Amir Abdollahian as saying.

At a regional security conference in Bahrain on Saturday, Saudi Foreign Minister Adel al-Jubeir said a major stumbling block to agreement at the Vienna talks had to do with the timing of the departure of Assad.

"The second has to do with the timing and the means of the withdrawal of foreign forces fromSyria – in particular, Iranian forces, which, incidentally, we view as an occupying force," Jubeir added.

Iran's Deputy Foreign Minister Amir-Abdollahian speaks during news conference in Moscow Thomson Reuters Before the meeting, Jubeir said Riyadh was participating to "test the intentions" of Iran and Russia and see if there was any possibility of them compromising over the fate of Assad.

Iran's Abdollahian said Jubeir was insisting that "those present in the meeting should decide the fate of the legal president of Syria ... instead of the Syrian people." He also denied that Iran had any combat forces in Syria.

"They are military advisers who went there at the request of Syrian regime to fight against terrorism," he said.

"We said that Iran has increased its presence in Syria in recent weeks. It's none of Saudi Arabia's business how the Islamic Republic is fighting against terrorism."

The number of Iranian casualties in Syria has risen in recent days. Iran's elite Revolutionary Guards Corps has confirmed deaths among its personnel in Syria.

Senior regional sources have told Reuters that hundreds of Iranian troops had arrived since late September to take part in a major ground offensive against rebels planned in west and northwestSyria, the biggest deployment of Iranian forces yet.

Russia entered the war on Sept. 30, launching a campaign of air strikes on rebel forces to help Assad retain core government territory in the west and south of the country.