MOSCOW - Russia, the only world power with close ties to the Syrian regime, urged President Bashar al-Assad on Friday to talk to the opposition as Moscow itself put out feelers to the rebels.

The new pressure on Assad came as Moscow revved up its bid to save a tattered peace process by first hosting a top Damascus envoy and then planning for a meeting Saturday with Syria peace mediator Lakhdar Brahimi.

Russia also invited the head of the opposition National Coalition for talks in either Moscow or a regional capital - the Kremlin's first contact with a group formed in November and recognised by the West as the sole legitimate representative of Syrians. But the opposition chief rejected the Moscow invitation for talks.

Moscow still views Assad as the legitimate leader, and its outreach to the regime's opponents found a cool response from the National Coalition chief.

Ahmed Moaz al-Khatib told Al Jazeera television that he would meet the Russians outside Moscow only on condition that they issued "a clear condemnation of the crimes committed by the Syrian regime."

The fast-paced but tricky diplomacy came as rebels pounded the Wadi Deif army base, one of the government's dwindling number of outposts in the northwest, the Syrian Observatory for Human Rights said.

Rebels on the ground said the jihadist Al-Nusra Front, blacklisted by Washington as a terror outfit, was leading the offensive.

Loss of the base would cut the main resupply route from the capital to second city Aleppo.

The Observatory said that at least 121 people were killed nationwide on Friday, 43 of them civilians.

Foreign Minister Sergei Lavrov said Russia still refused to back international calls on Assad to step down.

But he made explicit that Russia wanted Assad to put all options on the table after 21 months of violence that have claimed more than 45,000 lives.

"We actively encouraged... the Syrian leadership to maximally put into action its declared readiness for dialogue with the opposition," Lavrov told reporters when asked about his meeting on Thursday with Syrian Deputy Foreign Minister Faisal Muqdad.

He said Russia hoped to see Assad's government "underscore that they are open to discussing the widest range of items in line with the agreements reached in Geneva on June 30."

That accord - rejected by the opposition and never implemented because of the fighting - sought to quickly establish an interim coalition government but made no direct call on Assad to step down.

Meanwhile, two Syrian air force generals have defected from the regime of President Bashar al-Assad and joined opposition forces in Turkey, a diplomat said on Friday.

The generals, commanders of the Regional Air Force, have crossed the border and arrived in the town of Reylanli in southern Turkey, the Turkish diplomat told AFP on condition of anonymity.

The generals and dozens of lower-ranking officers and their families were taken to a separate camp where army defectors take refuge.

Turkish officials refuse to give an exact number of Syrian generals currently on Turkish soil as some are returning to Syria to join the active fighters inside the conflict-wracked country.

The latest defections come as Syrian rebel forces besiege Menagh air base northwest of Aleppo after months of clashes with loyalist troops.