The UN's special envoy to Syria has called for the government and the opposition to be involved in the latest attempt to bring political progress on ending the four-year civil war.

Speaking after a series of meetings with Syrian government members in the capital, Damascus, Staffan de Mistura said on Monday that all sides of the conflict should be involved in the process of finding a solution.

De Mistura arrived in Damascus on Sunday, two days after world powers and regional rivals met in Vienna to try to find a solution to the conflict that has left more than 200,000 dead and half of the population displaced.

"We have been discussing the aspects of the Vienna talks because the Syrian government was not present, neither was the opposition and I think it is very important that everyone, all Syrians should be involved and associated so that is my duty and I am doing it," de Mistura said.

Participants called for a nationwide ceasefire and the renewal of stalled UN-brokered talks between the government and the opposition.

The future of President Bashar al-Assad was one of the major sticking points for the nations involved in talks, attended by 17 countries, the EU and US.

Iran, which backs Assad, and Saudi Arabia, which supports rebels fighting him, were face-to-face for the first time since protests against Assad erupted in 2011.

On Monday, the Islamic Republic said it would quit Syria peace talks if it found them unconstructive, citing the "negative role" of Saudi Arabia, in the latest twist in a spat between the regional rivals.

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

Fighting continues

Days after his decision to deploy a small number of special operations troops to Syria, President Barack Obama said the US won't be putting Americans on the front-lines to fight the Islamic State of Iraq and the Levant.

Obama told NBC News that special forces have previously run missions in Syria. He said US troops won't be fighting in Syria the way they did in the Iraq War with "battalions and occupations".

Russian military intervention in the war, which began a month ago in the form of an air campaign in support of Assad's forces, has intensified the conflict and brought renewed urgency to international efforts to end it.

 Syrian rebels use caged captives as 'human shields'

Moscow and Tehran back Assad, while the US and its allies say he must leave power as part of any political solution.

Meanwhile, the fighting has continued inside Syria, with regime helicopters allegedly dropping barrel bombs across a number of suburbs in the southern city of Deraa.

Syrian government forces have also been bombarding opposition territory in Douma near Damascus - a regular target for air strikes.

On Monday, Russia's defence ministry spokesperson said the country's air forces hit 237 targets in Syria in the last two days.

"In the past 24 hours, 131 sorties have been carried out from Hmeymim airbase, hitting 237 terrorist targets in the provinces of Hama, Latakia, Homs, Damascus, Aleppo and Raqqa," Igor Lonashenkov, the Russian defence ministry spokesperson, said.

Source: Al Jazeera and agencies