A large explosion went off near an office of the ruling Baath party in Syria's second city of Aleppo on Friday evening, said the Syrian Observatory for Human Rights.

"A big explosion was heard near al-Jabiri Square. It targeted an office of the Baath party, according to initial reports," the Britain-based watchdog said in a statement.

Syria's authorities have refused to submit a report on torture in the country to a United Nations committee scheduled to discuss the situation there next week, its secretary said on Friday.

The Committee Against Torture monitors the implementation of the U.N.'s anti-torture convention by state parties and is currently meeting in Geneva.

Syrian troops killed a would-be suicide bomber in the northern city of Aleppo on Friday, a day after devastating bomb blasts in Damascus, state television reported.

"Syrian authorities have foiled an attempted suicide attack in al-Shaar area of Aleppo and killed the would-be attacker," the channel said.

The European Union is set to slap new sanctions on Syria, imposing an assets freeze and visa ban on two firms and three people, EU diplomats said Friday.

They said the measures targeting "mainly sources of revenue for the regime" would be decided at talks between EU foreign ministers next Monday.

Syrian forces killed at least 13 people as tens of thousands of protesters defied regime gunfire and took to the streets on Friday, a day after twin bombings killed dozens of people in Damascus, a monitoring group and activists reported.

Four people were killed in the central province of Hama, two in the northeastern province of al-Hasakeh, two in the southern province of Daraa, one in the central province of Homs and one in the northern province of Aleppo.

Iran on Friday condemned the latest deadly bomb blasts to reel its ally Syria in a 14-month-old uprising and accused Western powers of orchestrating them.

"The terrorist acts were guided by (global) arrogance and the enemies of free nations," First Vice President Mohammad Reza Rahimi said, quoted by state news agency IRNA, using the Islamic republic's term for Western powers.

The Syrian regime is trying to destroy the U.N.-brokered peace plan aimed at ending 14 months of conflict, opposition leader Burhan Ghalioun told reporters in Tokyo on Friday.

"The regime is now trying to kill this (Kofi) Annan plan, and by a new technique which is terrorism," Ghalioun said, a day after suicide bombers killed at least 55 people in horrific attacks in Damascus.

The U.N. Security Council on Thursday condemned the deadliest bomb attacks of Syria's 14-month uprising, urging all sides to stick to an international peace plan after at least 55 people were killed.

The Syrian government and opposition traded the blame for Thursday's twin suicide bomb attacks in Damascus, which also left nearly 400 people wounded in horrific scenes of carnage.

Syria's U.N. envoy said Thursday that British, French and Belgian nationals were among foreign fighters killed in the country's mounting conflict and that there was al-Qaida involvement.

The ambassador, Bashar Jaafari, told the U.N. Security Council that 12 foreign fighters had been killed and 26 detained in recent clashes with Syrian forces.

Syria said Thursday's suicide attacks that killed at least 55 people and wounded hundreds was the work of "terrorists" armed and funded by foreign organizations and media.

The foreign ministry made the accusation in a letter to U.N. Secretary General Ban Ki-moon hours after the deadliest bombing attacks of the country's 14-month uprising, which also wounded nearly 400 people in Damascus.