At least 25 people were killed and 46 wounded Friday morning when a bomb exploded in the Syrian capital, marking the second large-scale attack in the city in two weeks and escalating pressure on the Arab League as it prepares to decide whether to extend a monitoring mission in the turbulent country.

State news media reported that a suicide bomber detonated an explosive device at a busy intersection in the central Midan neighborhood of Damascus at a time when many people would have been heading to Friday prayers. The perpetrator was not immediately clear: As in the previous attack, officials blamed terrorists, while dissidents said the authorities themselves were responsible. Neither side cited evidence to support its claims.

Midan has been the site of numerous protests in the course of a nine-month uprising against the government of President Bashar al-Assad. The military crackdown in response to the revolt has killed at least 5,000 people, according to U.N. estimates, and Rami Abdulrahman of the Syrian Observatory for Human Rights said Friday that almost 300 civilians have been killed since Arab League monitors arrived nearly two weeks ago to oversee implementation of an agreement to halt deadly force against protesters.

Friday’s attack comes at a decisive moment for the 22-member Arab body, which is set to meet Sunday to decide whether to continue the mission in Syria — where roughly 100 monitors have deployed to the flash-point cities of Homs, Daraa and Hama — or to withdraw the team and perhaps refer the issue to the U.N. Security Council.

“I fear that the violence is going to escalate, especially in the absence of any credible dynamic to stop it,” said Salman Shaikh of the Brookings Institution in Doha, Qatar. “The Arab League mission, I believe, has failed, and is not likely to lead to the implementation of the agreement.”

Qatar’s prime minister, Hamad Bin Jasim al-Thani, told reporters in New York on Wednesday that “mistakes” had been made during the mission and that he had discussed with U.N. Secretary General Ban Ki-moon the possibility of “technical help” from the world body. Ban said Friday that “the U.N. stands ready to provide technical assistance,” including training, to the Arab League monitors.

Ausama Monajed, a spokesman for the prominent Syrian National Council opposition group, said he believed that Friday’s attack was staged by Assad’s government to support its assertion that the unrest in Syria stems from the actions of extremist groups and armed gangs.

“Of course the Arab League should move to the Security Council,” Monajed said. “The violence needs to stop by whatever means necessary.”

But because a strong Security Council resolution would probably draw vetoes from Russia and China, he added, the Arab League should make clear that it would also consider intervening militarily without U.N. backing.

Protests took place across Syria on Friday, despite further violence that activists said killed 19 people. Although demonstrators say they are still targeted by snipers if they attend protests, most heavy weapons and uniformed soldiers have been withdrawn from cities in the past two weeks, seemingly in response to the presence of Arab League monitors.

“The Arab League is not professional, and I feel like they are not going to continue the mission,” said Omar al-Khani, an opposition activist in Damascus. Nonetheless, he noted, there has been no shelling in restive cities such as Homs since the monitors arrived, and it has been possible to send food and supplies into opposition-dominated areas.

“If the monitors leave, the regime will start the attacks again,” Khani said.

U.S. officials say they are reluctant to publicly characterize the Arab League effort as ineffective, but the Obama administration hopes that the league will conclude that it cannot succeed without support from the United Nations and a far larger contingent of outside observers.

Russian officials this week floated their own resolution, which would urge a cease-fire on both sides and institute a ban on arms shipments to the opposition.

Russia has said that it, too, supports the Arab League initiative but wants the bloc to propose a plan for reconciliation and for a more gradual transfer of power that could leave Assad in office indefinitely. As the United States and Russia vie for influence, the league is divided over how to proceed.

In Damascus, residents of Midan have told of busloads of security forces arriving in the area every Friday, arresting and beating people departing mosques after prayers, some of them chanting anti-government slogans.

A Syrian security official told the Associated Press that the target of Friday’s bomb attack appeared to be a bus carrying police. Most of the casualties were civilians, according to the official Syrian Arab News Agency, which published images of shattered cars and bloodied corpses.

The Arab League’s deputy secretary general, Ahmed bin Heli, denounced the attack and said the observers would be able to contribute insight, the AP reported. “The mission, which is on the scene, will undoubtedly have an opinion,” he said.

Two weeks ago, also on a Friday, a double car bombing targeted security buildings in Damascus, killing 44 people, according to authorities. Such attacks were all but unknown in the capital until then.

Syrian authorities blamed the Dec. 23 bombing on al-Qaeda. But some Western diplomats expressed doubt that al-Qaeda could operate in a country as tightly controlled as Syria and suggested that either opposition groups or Assad’s government were probably responsible for that attack.

Leaders of the Free Syrian Army, a loose collection of defected soldiers that has taken responsibility for some attacks on security infrastructure in Syria, said the group played no role in either of the recent Friday bombings.

Col. Malik Kurdi, an assistant commander of the group, said by phone from Turkey: “These people in the square were opposition and preparing to demonstrate, so why would we kill them?”

Khani, the opposition activist in Damascus, said it would be virtually impossible for anyone to bring explosives into the city, especially on a Friday, because of heavy security and many checkpoints.

The Obama administration said Friday’s blast was clearly audible from the U.S. Embassy, less than two miles away. State Department spokeswoman Victoria Nuland said the administration did not know who was responsible for the attacks, which the United States has condemned.

Staff writer Karen DeYoung in Washington contributed to this report.