Extremists headed from Lebanon to Syria in the past few months to carry out more bombings and suicide attacks aimed at shaking the regime of Syrian President Bashar Assad, al-Akhbar newspaper reported on Friday.

Around five experts trained in preparing explosives left a Palestinian refugee camp in Lebanon heading to Syria, Islamist sources told the daily.

Saudi ambassador to Lebanon Ali Awadh Asiri lashed back at the head of the Syrian mission, Ali Abdul Karim Ali, for accusing Saudi Arabia and Gulf countries of arming the Syrian rebels and being responsible for the Syria-destined weapons shipment recently intercepted by Lebanese army.

“With all the respect I have for my colleague ambassador Ali Abdul Karim, I am surprised by his hasty statements in which he accused (Gulf) countries without any evidence,” the Saudi ambassador said in a statement.

The head of the U.N. military observer mission in Syria, Major General Robert Mood, said on Thursday that it was the responsibility of the Syrian army to make the first move to halt the violence.

"If you have two individuals using on each other all their weapons, who is going to be the first one to move the finger? Who is going to be the first one to make the move?" Mood asked, during a visit to the battered central city of Homs.

A terrorist haven in the eyes of the Syrian regime but "heart of the revolution" for its foes, Baba Amr is now a ghost town where residents move silently among the rubble of their homes.

Two months of bombardment reduced this central district of Homs city to nothing more than a heap of ruins. The walls of houses are pocked with bullets holes, punctured by tank shells and gouged by shrapnel.

Syria's Aleppo University on Thursday announced it was suspending classes after pro-government forces killed four students and arrested more than 200 in a campus raid during anti-regime protests.

In a message posted on its website, the northern city's university told students that classes were suspended until final exams on May 13.

Syrian security forces arrested two sons of prominent opposition figure Fayez Sara on Thursday, hauling them off to an unknown location without showing a warrant, he told Agence France Presse.

"Security forces stormed the apartment where the brothers live at 6 am (03:00 GMT). They broke down the door looking for weapons and took Bassam, 37, and Wissam, 26,” Sara told AFP by telephone.

Four students were killed overnight and 28 wounded as Syrian government troops and pro-regime gunmen raided the university campus in the northern city of Aleppo, a monitoring group said Thursday.

The Syrian Observatory for Human Rights said three of the wounded students were in critical condition and some 200 detained in the raid just after midnight.

The head of the U.N. mission to Syria said Wednesday his observers were having a "calming effect" on the ground but admitted the ceasefire was "shaky" and not holding.

Speaking in Damascus to Britain's Sky News, in his first television interview in the role, Major General Robert Mood brushed off criticism that the United Nations Supervision Mission in Syria (UNSMIS) had been too slow to get going.

Syria's economy is expected to contract significantly in 2012 due to 14 months of violence and sanctions, a top official at the International Monetary Fund said on Wednesday.

"We do expect contraction in GDP (Gross Domestic Product) this year," the head of the IMF's Middle East, North Africa, Gulf and Central Asia Department, Masood Ahmed, told Agence France Presse, adding that the drop is poised to be "significant".

A United Nations official is in Syria to assess the humanitarian needs in the strife-torn country, a spokesman for the U.N. mission in Damascus told Agence France Presse on Wednesday.

"Philippe Lazzarini, deputy to (U.N. humanitarian chief) Valerie Amos, is visiting Syria to coordinate with the Syrian government to assess humanitarian needs and direct distribution of aid," Khaled al-Masri said.