The world's chemical watchdog said Tuesday it will send a second team of inspectors to help dismantle Syria's arsenal, as regime warplanes bombed rebels in the northwest of the country.

Meanwhile Russia praised Damascus for "very actively" cooperating with the chemical weapons inspectors already on the ground.

The ongoing violence underlined comments on Monday from UN chief Ban Ki-moon, who warned that the weapons inspectors face unprecedented danger.

In a report to the UN Security Council, Ban said it would take 100 foreign experts to complete "an operation the likes of which, quite simply, has never been tried before."

On Tuesday, the Organisation for the Prohibition of Chemical Weapons (OPCW) said it would send a second team to Damascus to bolster an existing UN-OPCW group on the ground.

"That will augment the advance team of OPCW experts, who have been in Syria since 1 October conducting verification and destruction activities," it said, without providing further details on the new inspectors.

OPCW Director General Ahmet Uzumcu said the process of destroying Syria's chemical arsenal would be "long and difficult" but welcomed a "constructive beginning" to the operation.

The inspectors have until mid-2014 to verify and destroy Syria's chemical arsenal under the terms of a UN Security Council resolution that enshrines a US-Russian deal.

The deal averted threatened US military action in response to August 21 sarin gas attacks outside Damascus in which hundreds of people died.

Violence in the country has continued, with Syrian jets on Tuesday firing at rebels in the northwestern province of Idlib a day after they launched a major assault against two military bases.

The rebel operation dubbed "The Earthquake" is intended to capture the Wadi Deif and Hamidiyeh bases near the opposition-held town of Maaret al-Numan.

The Syrian Observatory for Human Rights said 10 regime troops and five rebels had been killed in the clashes.

Russian President Vladimir Putin meanwhile praised Syria's President Bashar al-Assad for his government's cooperation with a team of international weapons inspectors.

"Doubts about whether the Syrian leadership would adequately respond to the decision taken on chemical weapons -- these doubts did not bear out," Russian news agencies quoted Putin as telling reporters at a regional summit in Indonesia.

"The Syrian leadership has very actively joined this work and is acting in a transparent manner, helping international agencies," said Putin.

Ban: 'Dangerous' work for inspectors

On Monday, Ban warned of the dangers the inspectors face in Syria, where more than 115,000 people have been killed since March 2011, according to the Observatory.

The experts would have to work in "dangerous and volatile" conditions, particularly in urban areas such as Damascus, Homs and Aleppo, the UN leader warned.

"Heavy artillery, air strikes, mortar barrages and the indiscriminate shelling of civilian areas are commonplace and battle lines shift quickly."

Some 19 OPCW arms experts and 16 UN logistics and security personnel are in Syria and have started to destroy weapons production facilities.

Ban recommended the team be increased to about 100 scientists, logistics and security experts who will stay for up to a year.

The mission will have bases in Damascus and Cyprus.

Syria has already made a declaration of its weapons facilities. And the UN resolution set a November 1 deadline for the eradication of production and chemical mixing facilities.

That work started Sunday when the first "missile warheads, aerial bombs and mixing and filling equipment" were cut up and destroyed, according to the UN.

The Security Council resolution passed on September 27 threatened "measures" under Chapter VII of the UN Charter if an infringement of the disarmament accord is proved.

Chapter VII allows for possible military action or sanctions.

But US Secretary of State John Kerry has welcomed the progress made so far.

"I think it's extremely significant that yesterday, Sunday, within a week of the resolution being passed, some chemical weapons were being destroyed," he told reporters in Indonesia on Monday.

"I think it's a credit to the Assad regime, frankly. It's a good beginning and we welcome a good beginning."