At least 400 children have been killed in 11 months of violence in Syria and almost the same number detained, the United Nations Children's Fund (UNICEF) said on Tuesday.

"As of the end of January, 400 children are dead and more than 400 have been detained," UNICEF spokeswoman Marixie Mercado said at a briefing.

Ministers from the secular Iraqiya bloc on Tuesday ended a cabinet boycott that began in December amid a crisis with the Shiite-led government, Iraqi Prime Minister Nouri al-Maliki's spokesman said.

"The prime minister welcomed the return of the ministers to accomplish the work of the government," Ali Moussawi told Agence France Presse.

Russia's foreign minister said after Damascus talks on Tuesday that President Bashar al-Assad was "fully committed" to ending the bloodshed in Syria even as regime tanks pounded the central city of Homs for a fourth straight day.

Sergei Lavrov said he had had a "very useful" meeting with Assad and that Moscow was eager to work towards a solution based on an Arab League plan that it had previously criticized.

The Syrian opposition on Tuesday urged businessmen across the strife-torn country and throughout the Arab world to fund rebel forces seeking the overthrow of the regime of Bashar Assad.

"We are sending a warm appeal to Arab and Syrian businessmen to take part in an efficient and direct way in the legitimate financing of self-defense operations and the protection of civilian areas carried out by the Free Syrian Army," a joint statement issued by the Syrian National Council and the FSA said.

Vandals scrawled anti-Arab and anti-Christian slogans on a monastery and a school in Jerusalem overnight, Israeli police said on Tuesday.

Police spokesman Micky Rosenfeld said unknown people sprayed graffiti reading "death to Christians" and "price tag" on the walls of the Greek Orthodox Monastery of the Cross in west Jerusalem overnight.

At least 21 civilians and four soldiers were killed on Tuesday in violence across Syria, the majority of them in the flashpoint central city of Homs, activists said.

"At least nine civilians, including a woman, were killed by gunfire and shelling as (troops) attempt an assault on the Khaldiyeh neighborhood of the city," the Syrian Observatory for Human Rights said in a statement.

Iran said on Tuesday foreign interference would destabilize Syria, rejecting accusations that Tehran was complicit in a "massacre" of civilians by supplying weapons to its main ally's forces.

"We are absolutely not interfering in the internal affairs of Syria, and we consider that the interference of other countries there to be a danger to the security and stability of Syria," foreign ministry spokesman Ramin Mehmanparast told reporters.

Eleven Iranian pilgrims recently abducted in restive Syria have been freed, an Iranian foreign ministry spokesman said on Tuesday without speaking of the fate of more than a dozen other captive Iranians there.

"With the aid of friendly countries... 11 pilgrims have been released," foreign ministry spokesman Ramin Mehmanparast told reporters in his regular weekly briefing, without giving further details.

Syria's government vowed Tuesday to push forth with its onslaught on the central province of Homs in a bid to rid the region from what it said were "armed terrorist gangs".

"Operations to hunt down terrorist groups will continue until security and order are reestablished in all neighborhoods of Homs and its environs and until we overcome all armed persons terrorizing citizens and threatening their life," the interior ministry said in a statement carried by SANA state news agency.

The British-born wife of Syria's president has spoken in support of her husband for the first time since the 11-month uprising against his regime began, a British newspaper reported Tuesday.

"The President is the President of Syria, not a faction of Syrians, and the First Lady supports him in that role," The Times quoted Asma Assad as saying in an email sent via an intermediary from her office.