Israeli Defense Minister Ehud Barak on Thursday accused Iran of "exaggerating" progress on its disputed nuclear program a day after Tehran unveiled what it said was its first domestically-produced 20-percent enriched uranium.

"The Iranians are continuing to progress but what they presented yesterday was a show. There are many things which have been presented in an exaggerated manner, partly to dissuade the world from going after them," he told public radio by telephone from Tokyo.

Syrian armor moved on the main hubs of an 11-month uprising on Thursday killing at least 22 people, monitors said, a day after President Bashar Assad set a vote for a new constitution.

Opposition groups rejected the newly proposed constitution and urged voters to boycott a referendum set for this month, and to step up efforts to oust Assad.

Seventeen Yemeni tribesmen were killed Thursday in clashes that followed the assassination of a local al-Qaida leader by his half-brother in his stronghold southeast of Sanaa, tribal chiefs said.

The clashes erupted after Tarek al-Dahab was shot dead by his half-brother Hizam in the town of al-Masaneh, a family fiefdom in Bayda province, several tribal chiefs said, confirming that the killer and his brother were among the 17 killed in the gunfights.

At least eight Palestinian children were killed on Thursday when an Israeli truck hit a Palestinian school bus on a road in the West Bank, Israeli police said.

"There are between eight and 10 Palestinian children dead, aged between 10 and 16, and more than 30 injured who were taken to various hospitals in Ramallah and Mt Scopus," police spokeswoman Luba Samri told Agence France Presse.

China said Thursday it is sending an envoy to Syria to push for a "peaceful" resolution of the conflict there, after drawing condemnation for vetoing a resolution condemning a crackdown on protesters.

Vice Foreign Minister Zhai Jun will visit Syria from February 17 to 18, foreign ministry spokesman Liu Weimin told a regular briefing.

A Syrian opposition group on Thursday rejected a newly proposed constitution, urging voters to boycott a referendum set for later this month and to step up efforts to oust President Bashar Assad.

"The Local Coordination Committees calls upon our people to reject and boycott the alleged referendum to confirm the lack of public support for this criminal regime," the opposition group said in a statement.

Israeli warplanes early Thursday carried out two raids on the north and center of the Gaza Strip following a rocket attack on southern Israel, an army spokeswoman said.

The attacks, which came after an Israeli police spokesman said three rockets had been fired from the Gaza Strip without claiming victims, were aimed at "centers of terrorist activity," the army spokeswoman said.

Seven Iranian engineers kidnapped near Syria's embattled city of Homs in late December have not been released as previously reported, and remain captives, the Iranian foreign ministry said on Thursday.

"We hope to witness the freedom of the Iranian engineers and the rest of pilgrims soon," ministry spokesman Ramin Mehmanparast was quoted as saying by the Fars news agency.

Switzerland Wednesday said it was closing its embassy in Damascus and urged its nationals to leave Syria "as quickly as possible".

The embassy closure, which follows that by the United States, was announced by Swiss Foreign Minister Didier Burkhalter and comes against a background of increasing violence inSyria where the regime is seeking to crush a nearly year-long rebellion.

Turkey urged the United Nations on Wednesday to appeal to the Syrian leadership to allow a humanitarian operation to help Syrians suffering from the months-long bloodshed.

Speaking to reporters, Foreign Minister Ahmet Davutoglu said the U.N. should step in not only on political matters "but also on humanitarian issues," vowing that Turkey would keep the Syrian crisis "on the U.N. agenda."