Syria was hit by a lethal car bombing on Sunday, the third in two days, ahead of a mission sent by special envoy Kofi Annan for talks on a monitoring operation to end a year of bloodshed.
Technical experts from the United Nations and Organisation of Islamic Cooperation, meanwhile, have started a mission to assess the humanitarian impact of the conflict, a senior OIC official said on Sunday.
State media, charging that such bombings aim to sabotage efforts to find a political solution to Syria's crisis, said Sunday's blast in Aleppo killed two people, including a woman, and wounded 30 others.
State television showed heavy damage to apartment buildings and private cars, while the Syrian Observatory for Human Rights said the attack targeted political security offices.
Aleppo, the second largest city in Syria and its commercial hub, was the target of car bombings on February 10 that killed 28 people.
On Saturday, twin car bombings killed 27 people and wounded 140 others in the heart of Syria's capital, mostly civilians, the interior ministry said, blaming "terrorists" for the attacks near police and air force headquarters.
Damascus and Aleppo are both seen as having high levels of support for President Bashar al-Assad.
"Yesterday's explosions were carried out by terrorists supported by foreign powers which finance and arm them," charged Al-Baath newspaper, mouthpiece of Assad's ruling party of the same name.
"The two attacks... aim to disrupt Annan's mission and to foil international efforts to find a political solution to the crisis," it said, referring to UN-Arab League peace envoy Annan.
Ath-Thawra, another official daily, pointed the finger at Qatar and Saudi Arabia which have called for rebels fighting the Assad regime to be armed.
The opposition Syrian National Council accused the regime of staging the weekend's deadly car-bomb attacks to terrorise its own citizens and for Syria to be viewed as under threat from Al-Qaeda, calling for an international commission of inquiry.
Technical experts from the UN and OIC, meanwhile, were taking part in a mission to assess the humanitarian impact of the regime's deadly crackdown on protests since March 2011.
"The joint OIC-UN mission entered Syria on Friday to carry out an evaluation of humanitarian aid," on a mission led by the Syrian government, its assistant secretary general, Atta al-Mannan Bakhit, told AFP.
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He said the mission, with three OIC experts in the team, would cover 15 cities, after which a report would be submitted to the Saudi-based Islamic grouping and the United Nations on the humanitarian needs of the Syrian population.
UN humanitarian chief Valerie Amos, who held talks in Damascus earlier this month, has said the experts would join the assessment mission to Daraa, Homs, Hama, Tartus, Latakia, Aleppo, Deir Ezzor and rural zones around Damascus.
The UN experts and staff of the 57-member OIC would "accompany the mission and take the opportunity to gather information on the overall humanitarian situation and observe first-hand the conditions in various towns and cities," she said.
The United Nations estimates that more than 30,000 Syrians have fled to neighbouring states and another 200,000 have been displaced within the country by the past 12 months of deadly violence.
Activists say the year-long conflict has cost more than 9,100 lives.
In parallel with the mission, international Red Cross chief Jakob Kellenberger is to hold talks with Russian Foreign Minister Sergei Lavrov in Moscow on Monday on the "extremely difficult" humanitarian situation in Syria's protest centres.
"A daily ceasefire of at least two hours is imperative to allow the evacuation of the wounded," he said ahead of the mission to Moscow, an ally of Damascus which is seen as having influence on Syria's leadership.
Former UN chief Annan, who met Assad in Damascus last weekend, has also ordered a team of experts to Syria to discuss a possible ceasefire and international monitoring mission, his spokesman said.
Annan's team will head to Damascus from New York and Geneva on Monday.
In violence on the ground, raids by security forces killed three civilians, including a 14-year-old boy, in the Jabal al-Zawiya region of Idlib in the country's northwest, said the Syrian Observatory, a Britain-based monitoring group.
The Observatory said four soldiers were killed in clashes with rebels in the same region bordering Turkey, while security forces killed a civilian in Daraa, where deserters blew up a bridge near Khorbet al-Ghazaleh to cut off a supply route.
It also reported that security forces beat up and detained opposition figure Mohammed Sayyed Rassas, a National Coordination Committee for Democratic Change leader, which is normally tolerated, and several youths at a Damascus protest.
On Saturday, two "terrorists" were killed when a booby-trapped car they were driving blew up in a Palestinian refugee camp in a suburb of Damascus, the state news agency reported.