An al-Qaeda-affiliated organization has asserted responsibility for a deadly wave of bombings in Baghdad last week, according to a monitoring group, in what analysts said Tuesday marked a bid to inflame sectarian divisions in a country rocked by political tension.

The Islamic State of Iraq described a bomber as “one of the heroes of the Sunnis” and a Shiite militia as “filthy” in messages it posted Monday on Internet forums monitored by the SITE Intelligence Group.

“The terrorists are certainly exploiting the political situation and are making it more poisonous — and sectarian,” said Reidar Visser, an Iraq expert at the Norwegian Institute of International Affairs.

Political strife has been building for weeks in Iraq between Shiite Prime Minister Nouri al-Maliki and Sunni leaders. On Dec. 18, the last U.S. troops departed. On Dec. 19, an official from the Maliki-controlled Interior Ministry announced on national television that judges had issued an arrest warrant accusing the Sunni vice president of terrorism.

The vice president, Tariq al-Hashimi, denies the charges and has fled Baghdad for the semiautonomous region of Kurdistan. Maliki has demanded the Kurds hand him over.

“We thought he would try to build his power more slowly over time. This was an instant confrontation,” said Anthony Cordesman, an analyst at the Center for Strategic and International Studies, referring to Maliki.

On Thursday morning, at least 15 bombs were set off over a two-hour period, killing at least 65 people. The Islamic State of Iraq called it a “Thursday Invasion” on Web forums Monday and bragged about bombing a building that housed an agency charged with investigating government corruption. The group labeled the building a “despicable den.”

“What they want is to provoke a sectarian struggle, a conflict that potentially involves other countries in the region,” Cordesman said, noting that Maliki effectively runs the Interior Ministry’s security forces. Although the agency has more than 640,000 members, Cordesman calls it “in many ways a hollow force” that is seen in Iraq as a massive government-jobs program.

Another Iraq analyst, Joel Rayburn of the National Defense University in Washington, said the magnitude of last week’s attack surprised him.

“It takes hundreds of people to pull that off, spread across the city,” he said, noting that he was speaking for himself and not the university. “Safe houses, lookouts, planners, logisticians, communicators, bombmakers, people inside the security forces — a very extensive network of these people, plus sympathizers, to carry off a dozen coordinated bombings.”