ISLAMABAD, Pakistan —Denmark’s intelligence service cast blame on Al Qaeda for an attack near its embassy in Pakistan that investigators said today was carried out by a suicide bomber.

No one has claimed responsibility for the car bomb, which killed six people. But Danish authorities said the terror network or one of its affiliates was likely behind the explosion, which came just weeks after the terrorist group threatened Denmark over caricatures of the Prophet Muhammad reprinted earlier this year in newspapers in that country.

“It is (the Danish Security and Intelligence Service’s) assessment that Al Qaeda or an Al Qaeda-related group likely is behind the attack,” Jakob Scharf, director of the agency, said. He added that “a series of other militant Islamic groups and networks in Pakistan also could have the intention and the capacity to hit Danish targets in Pakistan.”

A team of Pakistani investigators sifted through the rubble at the scene of the explosion in a leafy neighborhood of Islamabad where security is supposed to be tight. Danish experts were expected to join them.

“I think we can say with a reasonable degree of confidence that it was a suicide attack,” the director general of the Federal Investigation Agency, Tariq Pervez, said.

That conclusion could strengthen suspicions Al Qaeda or an associated group was involved.

Mr. Pervez said the bomb, containing about 55 pounds of explosives, was similar to that used in a suicide bombing in the eastern city of Lahore in March.

Authorities have provided no results of the investigation into that attack, and Mr. Pervez declined to discuss who might have been responsible for yesterday’s blast.

But the Danish intelligence agency said in a statement late yesterday that the embassy was probably the target.

The explosion wounded at least 35 people, left a deep crater on the road outside the embassy, severely damaged the nearby office of a development group, and devastated trees and cars. The embassy building remained standing, though its windows were shattered.

The six dead include two Pakistani policemen, a cleaner, and a handyman employed by the embassy. One was Pakistani-born with a Danish passport, the Foreign Ministry in Copenhagen said.

A senior city police officer, Ahmed Latif, said the attacker used a stolen car with a fake diplomatic license plate to get past security near the embassy. He said several people were being questioned about the ownership of the car, but they were not regarded as suspects. No one has been arrested, he added.

Denmark has faced threats at its embassies following the reprinting in February by about a dozen newspapers of a cartoon that depicted Muhammad wearing a bomb-shaped turban. That and other images in a Danish paper sparked riots in the Muslim world in 2006.

Denmark’s Berlingske Tidende daily lashed out at Pakistan in a comment titled “Pakistan’s poor security.”

“We have simply trusted the Pakistanis’ ability to protect us too much,” it said.

The explosion could heighten pressure on Islamabad to stop striking peace deals with militants in the border regions, where Al Qaeda and Taliban fighters are believed to have found sanctuary.

Pakistan insists it is not talking to “terrorists” but rather militants willing to lay down their weapons. But America has warned the deals could simply give militants time to rebuild strength.

The Prime Minister of Pakistan, Yousuf Raza Gilani, said in a statement yesterday the blast would “redouble our resolve” to “continue on our avowed path to fight terrorism and extremism.” Interior Ministry chief Rehman Malik said the attack would not affect the peace talks.

The CEO of IntelCenter, an American group that monitors Al Qaeda messages, Ben Venzke, said the terror group called for attacks against Danish diplomatic facilities and personnel in a video last August, and repeated its threat in April.

“I urge and incite every Muslim who can harm Denmark to do so in support of the Prophet, God’s peace and prayers be upon him, and in defense of his honorable stature,” IntelCenter quoted the Al Qaeda No. 2, Ayman al-Zawahri, as saying in an April 21 video.

But analysts said it was possible groups other than Al Qaeda who also were angry about the cartoons could be behind the blast. Islam generally forbids any depiction of the prophet, even positive, for fear it could lead to idolatry.

A former security chief for the tribal regions, Mahmood Shah, said Al Qaeda attacks tend to be more lethal. He said that if the attack was a suicide bombing, it likely originated in the unruly border regions.

Even if the attack isn’t linked to the tribal regions, the Americans and the West “will use this … to say look, your policy (on peace deals) is not working,” an analyst, Talat Masood, said.

Yesterday’s attack follows a bombing in March at a restaurant in Islamabad that killed a Turkish aid worker and wounded at least 12 others, including at least four FBI personnel.