Syria threatened on Thursday an immediate response to any new Israeli strike, after two reported attacks on military targets, as its Lebanese ally Hezbollah said Damascus would arm it with 'game-changing' weapons despite those strikes.

Damascus also welcomed a US-Russian initiative to find a political solution to end the two-year-old civil war, though again balking at Washington's demand that President Bashar al-Assad would need to stand down.

And it said it was ready to receive a UN team to probe claims that chemical weapons had been used in the country.

In an exclusive interview with AFP, Deputy Foreign Minister Faisal Muqdad said "the instruction has been made to respond immediately to any new Israeli attack without (additional) instruction from any higher leadership, and our retaliation will be strong and will be painful against Israel."

Senior Israeli sources have said strikes on early Friday and Sunday targeted weapons bound for the powerful Lebanese Shiite group Hezbollah, but Muqdad denied that.

"They absolutely did not achieve their objective and they lied when they said they are targeting Hezbollah," he said, adding there is "no way Syria will allow this to happen again."

In Beirut, Hezbollah chief Hassan Nasrallah said Syria would supply his movement with "game-changing weapons" and open up the front to "resistance fighters" against the Jewish state on the Golan Heights.

Israel captured the Golan from Syria in the 1967 Six-Day war and subsequently annexed it.

"You Israelis say your objective is to stop the capability of the resistance (against Israel) from growing... but Syria will provide (Hezbollah) with game-changing weapons it has not had before," Nasrallah said in his televised speech.

"If you (Israel) see Syria as a corridor of arms to (Hezbollah), Syria will provide the resistance with those arms. This is a highly strategic decision."

Israel has repeatedly warned it will intervene to prevent the transfer of advanced weaponry to Hezbollah, with which it fought a devastating 2006 war.

Hezbollah is battling alongside Assad's troops in several parts of the country.

The regime is relying increasingly on its alliance with Hezbollah, and Lebanese newspaper Al-Akhbar quoted Assad on Thursday as saying Syria would "give Hezbollah everything" for its loyalty.

The military and the Syrian Observatory for Human Rights watchdog both reported on Thursday that loyalist forces, including elements of Hezbollah, had advanced in the Qusayr area, which is strategically located along the Lebanese border.

Observatory chief Rami Abdel Rahman said the army's campaign was "fierce."

An army officer told AFP the military seized control of Shumariyeh village near Qusayr "and troops are currently on their way to the village of Ghassaniyeh" which has been under rebel control for more than a year.

Meanwhile, Syria's foreign ministry welcomed the US-Russian "rapprochement," under which the two countries will seek to convene an international conference to build on a six-point accord agreed in Geneva last year.

The Geneva agreement aimed at finding a path towards a transitional government but made no mention of Assad's departure, which the opposition says is non-negotiable.

US Secretary John Kerry said Assad would have to step down as part of the resolution to the conflict.

That was rejected by the Syrian foreign ministry, which stressed that the decision belongs "only" to the Syrian people.

And the ministry said it was "confident that the Russian position, which is based on the principles of the UN Charter and international law, will not change."

Russia is a top ally of the regime in Damascus and has staunchly resisted any bid to oust Assad.

Meanwhile the United Nations said its Syria envoy, Lakhdar Brahimi, has withdrawn a threat to quit and will stay the course in light of the US-Russian agreement.

And the Wall Street Journal reported that Israel had informed Washington about the imminent sale to Syria of Russian S-300 missile batteries, advanced ground-to-air weapons that can take out aircraft or guided missiles.

Reacting to the report, Kerry warned in Rome that the sale would be "potentially destabilising" for the region.

Moscow has continued to supply Damascus with weapons throughout the conflict, which has left more than 70,000 people dead since March 2011.

Under mounting international pressure over the possible use of chemical weapons, Syria said it was ready to receive a UN team to investigate the claims.

"We were ready and we are always ready, right now, to receive the delegation that was set up by Ban Ki-moon to investigate what happened in Khan al-Assal," Muqdad said, referring to a village near Aleppo where authorities say rebels used chemical weapons killing 30 people.

He added that the use of chemical weapons is a "red line for President Assad."