DAMASCUS, Syria — A bomb exploded Friday at a busy Damascus intersection, killing 25 people and wounding dozens in the second major attack in the Syrian capital in as many weeks, officials said, vowing to respond to further security threats with an "iron fist."
The government blamed "terrorists," saying a suicide bomber had blown himself up in the crowded Midan district. But the country's opposition demanded an independent investigation, accusing forces loyal to the Syrian regime of being behind the bombing to tarnish a 10-month-old uprising against President Bashar Assad.
"Is there anything worse than these crimes?" said Majida Jomaa, a 30-year-old housewife who ran to the streets after hearing the explosion around 11 a.m. "Is this freedom?"
It was impossible to determine the exact target of the blast, but a police bus was riddled with shrapnel and blood was splattered on its seats, according to Syrian TV video and a government official. Blood also stained the street, which was littered with shattered glass.
The bomber "detonated himself with the aim of killing the largest number of people," Interior Minister Mohammed Shaar told reporters. State media said most of the dead were civilians but security forces were also among them.
Midan is one of several Damascus neighborhoods that has seen frequent anti-Assad protests on Fridays since the uprising began in March, inspired by the revolutions around the Arab world.
The violence marks a dramatic escalation of bloodshed in Syria as Arab League observers tour the country to investigate Assad's bloody crackdown on dissent. The monitoring mission will issue its first findings Sunday at a meeting in Cairo.
In a statement, the Interior Ministry vowed to respond to any security threats with an "iron fist."
Syria's state media, SANA, put the initial death toll at 25 and more than 60 wounded. The death toll included 10 confirmed dead and the remains of an estimated 15 others whose bodies had yet to be identified.
"I found bodies on the ground, including one of a man who was carrying two boxes of yogurt," Midan resident Anis Hassan Tinawi, 55, told the AP.
The blast came exactly two weeks after twin bombings targeting intelligence agencies in Damascus killed 44 people. The regime blamed terrorists for those explosions as well.
A Syrian official, speaking on condition of anonymity because he was not allowed to talk publicly to the media, said a smaller bomb exploded Friday in the Damascus suburb of Tal, killing a girl. Security experts dismantled another bomb nearby, he said.
While many of the anti-government protests sweeping the country remain peaceful, the uprising as a whole has become more violent in recent months as frustrated demonstrators take up arms to protect themselves from the steady military assault. An increasing number of army defectors also have launched attacks, killing soldiers and security forces.
The unrest has posed the most serious challenge to the Assad family's 40-year dynasty. The regime's crackdown has led to broad worldwide condemnation and sanctions, eviscerated the economy and left Assad an international pariah just as he was trying to open up his country and modernize the economy.
The protests continued Friday around the country, and security forces killed at least eight people, according to the British-based Syrian Observatory for Human Rights. The Local Coordination Committees, another activist group, put the death toll at 11.
The Observatory said 50,000 protesters took to the streets in the Damascus suburb of Douma in the largest protest of the day. The numbers were impossible to confirm, however, because Syria has banned most foreign journalists and prevented independent reporting.
Also Friday, SANA said terrorists blew up a pipeline that carries diesel from the central province of Homs to nearby Hama. There have been several pipeline blasts in recent months, but it is unclear who is behind them.
The government has long contended that the turmoil in Syria is not an uprising but the work of terrorists and foreign-backed armed gangs.
In a sign of just how polarized Syria has become, the opposition questioned the government's allegations that terrorists were behind Friday's attacks and the Dec. 23 bombings.
Opposition leaders suggest the regime itself could have been behind the violence to try to erode support for the uprising and show the Arab League observers that it is a victim in the upheaval. Neither the regime nor the opposition has produced evidence backing their accusations, and no one but Syrian authorities have access to investigate the blasts.
A spokesman for the Syrian National Council opposition umbrella group called for an independent investigation.
"It is a continuation of the regime's dirty game as it tries to divert attention from massive protests," spokesman Omar Idilbi said. "We call upon for an independent international committee to investigate these crimes that we believe that the regime planned and carried out."
The Arab League observers started work Dec. 27 on a mission to monitor Syria's compliance with a League-drafted peace deal. Under the deal, Assad's regime is supposed to pull its military off the streets and stop its crackdown on protesters.
Despite the observers' presence, violence has spiked, with Syrian activists saying up to 400 people have been killed since Dec. 21. The U.N. says the overall death toll since the revolt began is more than 5,000.
Arab League Deputy Secretary-General Ahmed bin Helli condemned Friday's attack.
"We are concerned about these explosions. That is why we are calling on the Syrian government to be totally cooperative with the mission and to work by all means to stop the bloodshed and allow room for the political process to begin," he told The Associated Press in Cairo, where the League is based.
Bin Helli said the observers will have insight into the attack.
"The mission which is on the scene will undoubtedly have an opinion," he said.
Opposition groups have been deeply critical of the Arab League mission, saying it is giving Assad cover for his crackdown. The observer mission's Sudanese chief has raised particular concern because he served in key security positions under Sudanese President Omar al-Bashir, who is wanted for crimes against humanity in Darfur.
Critics also say the mission is far too small — and too dependent on government escorts — to be effective. The regime says the escorts are vital to the monitors' personal safety.
Salman Shaikh, director of The Brookings Doha Center in Qatar, said it was impossible to determine who was behind the attack, even with the Arab League observers offering an outside perspective.
"This again points to the need to have full independent credible investigation," he told the AP.
"I would actually say on the eve of the Arab League meeting, the Arab League mission is failing," he added. "It is failing to protect civilians. We have not had a halt to the violence. I think the Arab League now needs to go to the United Nations and seek a helping hand from the international community."
• AP writers Albert Aji in Damascus and Sarah El Deeb in Cairo contributed to this report.