At least 26 children were killed in violence in Syria on Monday, a watchdog said, fueling international calls for a war crimes probe into the 22-month conflict.

Reports of the child deaths came as Human Rights Watch accused President Bashar Assad's regime of expanding its use of banned cluster bombs.

Rape has been a "significant" weapon of war in the conflict raging in Syria since March 2011 and is the "primary" factor in the exodus of women and children refugees to neighboring Jordan and Lebanon, an aid group said on Monday.

In its report, "Syria: A Regional Crisis," the U.S.-based International Rescue Committee (IRC) described rape "as a significant and disturbing feature of the Syrian civil war".

Syria's regime has resorted to firing rockets containing cluster bombs, marking an expansion in its use of the banned munitions despite international condemnation, Human Rights Watch said on Monday.

The New York-based HRW has previously reported Syrian forces using air-dropped cluster bombs but in its latest statement said this had been expanded to the use of ground-based methods to spread the weapons.

The Senior Adviser to the Turkish President Abdullah Gul, Arshad Hurmuzlu, stressed on Monday that the case of the kidnapped Lebanese pilgrims in Syria is a local affair, pointing out that efforts are ongoing to free the men.

“It is wrong to deal with the case on the basis that it's a Lebanese-Turkish affair,” Hurmuzlu told An Nahar newspaper.

Russia said Sunday that removing Syrian President Bashar Assad from power was not part of past international agreements on the crisis and was impossible to implement, as violence across the country killed at least 100 people according to a rights group.

"This is a precondition that is not contained in the Geneva communique (agreed by world powers in June) and which is impossible to implement because it does not depend on anyone," news agencies quoted Russian Foreign Minister Sergei Lavrov as saying.

Lebanon appealed on Sunday for $180 million from Arab countries to help it meet the Syrian refugee influx that has threatened to bring the number of the displaced to 420,000 in June, as the Arab League decided to send a team to Syria's neighboring countries to assess the status of refugees ahead of a donor conference in Kuwait on January 30.

Arab foreign ministers meeting in Cairo to discuss the Syrian refugee crisis agreed to send a team to Lebanon, Jordan and Iraq "to assess the situation of Syrian refugees on the ground," the Arab League said.

Official media in Syria renewed attacks on U.N. and Arab League envoy Lakhdar Brahimi on Sunday, calling him biased and saying his peace mission aimed at solving the country's crisis was "useless."

On Wednesday, Brahimi criticized as "one-sided" a proposal by President Bashar Assad to end the crisis, and two days later he met top U.S. and Russian officials and urged "a speedy end to the bloodshed" in the strife-torn country.

Syria's army sent shells smashing into rebel zones on the outskirts of Damascus Sunday while a Palestinian camp south of the capital was rocked by fresh fighting, a watchdog said.

"Regime troops shelled Daraya, Beit Sahm, Mleha and Moadamiyat al-Sham," said the Syrian Observatory for Human Rights, referring to rebel-held towns dotted around the edges of Damascus.

More than 200,000 Syrian refugees have fled the bloody conflict in their home country for Lebanon, according to figures released by the United Nations High Commissioner for Refugees on Saturday.

“195,000 Syrians are currently receiving aid from the Lebanese government, the United Nations and non-governmental organizations,” a statement released by the U.N. said.

Switzerland will on Monday file a petition signed by 52 countries calling for the International Criminal Court (ICC) to open a case on war crimes in Syria, its foreign minister said.

"Serious war crimes are being committed in Syria. We must make sure they not go unpunished," Swiss Foreign Minister Didier Burkhalter told Swiss national television TSR on Friday.