Syria's government says two suicide attacks on security sites in the capital, Damascus, have killed and injured scores of civilians and soldiers.
Syrian reports say at least 40 people were killed and more than 100 wounded in the attacks, which were carried out in an upscale neighborhood. They targeted the main headquarters of the General Intelligence Agency and a branch of the military intelligence, two of the most powerful of Syria's multiple intelligence bodies.
Witnesses said one bomber tried to ram a vehicle packed with explosives into the compound of the General Intelligence Agency at around 10:15 local time before a second blew vehicle blew up within minutes outside the second intelligence building.
The Syrian Observatory For Human Rights, which is based in London, said witnesses reported heavy gunfire after the explosions.
Deputy Foreign Minister Faisal Mekdad told journalists that "terrorists" were responsible for the attacks.
Syrian State TV said initial investigations indicated possible involvement by Al-Qaeda.
The unprecedented blasts came a day after an advance team of Arab League observers arrived in the country to monitor Syria's promise to end its deadly crackdown on protesters demanding the ouster of President Bashar al-Assad.
Mekdad and other government officials took the observers to the scene of the explosions, citing them as evidence to their longtime claims that the recent unrest in Syria is not due to a largely peaceful popular uprising, but the work of terrorists.
Meanwhile, Omar Idilbi, a member of the Syrian National Council, an umbrella opposition group, suggested the regime was using the blasts to try to influence the Arab League team.
He called the explosions, "very mysterious because they happened in heavily guarded areas that are difficult to be penetrated by a car."
Joshua Landis, a Syria expert and the director of the Center for Middle East Studies at the University of Oklahoma, said the day's attacks do "play into the hands" of the Assad government.
"I think the Syrian government is probably guilty of trying to paint an Al-Qaeda picture of the opposition. It has been trying to accuse the opposition of being a bunch of Salafists and Al-Qaeda people from the beginning,” Landis said.
WATCH: The aftermath of the suicide bombings in Damascus
Reacting to the attacks, U.S. State Department spokesman Mark Toner said in a statement, "There is no justification for terrorism of any kind and we condemn these acts wherever they occur."
"It is crucial that today's attack not impede the critical work of the Arab League monitoring mission to document and deter human rights abuses with the goal of protecting civilians," he said.
A spokesman for UN Secretary-General Ban Ki-moon said he was "gravely concerned at the escalating violence in Syria."
Peaceful protests began in the country in March, and were seen as part of the Arab Spring protests that swept the Middle East and North Africa. But amid a violent government crackdown on dissent, the situation has steadily evolved into an armed conflict pitting the Syrian armed forces against opposition military units, whose ranks are bolstered by defectors.
Today's blasts were the first suicide bombings in Syria since the uprising began, and are considered unprecedented for striking close to the heart of Assad's regime.
The United Nations estimates more than 5,000 people, mostly civilians, have been killed in Syria since March. Damascus says 2,000 of its security personnel and soldiers have been killed in that period.
The Assad regime's lethal response to protesters has so far failed to crush the uprising.
Landis says that today's blasts may be an indication of sectarian tensions increasingly playing a part in the recent turmoil. Syria is a majority Sunni country, but Assad and his inner circle belong to the Alawite sect of Shi’ite Islam.
"In many ways, what we've seen in Iraq in the last few days and what we saw in Lebanon a few decades ago is probably going to come to Syria as well,” Landis said.
“The struggle in Syria is becoming increasingly sectarian-based. The Alawite and Ba’athist core of the regime is standing together, but increasingly the Sunni rank and file of the army are finding ways to defect or not show up to work. The religious undertones of this uprising are becoming stronger."
Meanwhile, activists said some 29 people were killed on December 23 in the flashpoint central city of Homs and the northern city of Idlib.
Homs, a Sunni-majority city and rebel stronghold, has been under a virtual military siege for months.
Also on December 23, Canada announced new sanctions against Syria, freezing government assets and prohibiting most trade with the country.
Washington and Brussels have also imposed sanctions on Damascus in response to the government crackdown.
with agency reports