BAGHDAD — A suicide truck bomber devastated the security headquarters of one of Iraq’s most peaceful cities yesterday, killing at least 15 people, wounding more than 100 and showing that no corner of Iraq is immune from violence.It was the first major attack in Irbil, the capital of the Kurdish self-governing region, in more than three years. The victims were among 72 people killed or found dead nationwide.

The Islamic State of Iraq, an al-Qaida front group, claimed responsibility for the Irbil blast, saying it was in retaliation for the Kurdish regional government’s decision to send Kurdish troops to Baghdad to take part in the security crackdown in the capital.

The claim, posted on an Islamic extremist website, could not be verified. If true, it would be the first known attack by the Islamic State so far north. Most of the group’s operations have been in Baghdad and the provinces of Anbar and Diyala.

The explosion in Irbil, a mountainous city of 1.5 million people about 215 miles north of Baghdad, blew out all the windows of the three-story Interior Ministry building and left piles of rubble and twisted metal beams.

Police said a truck loaded with a ton of explosives under detergent and shampoo containers exploded while it was between two buildings. The road was packed with vehicles because of construction work.

Ahmed Nasruldin, 50, an employee at a local university, was riding to work when the blast spun his bus around.

“The bus windows were smashed and my face and head were hurt by shrapnel. A woman beside me fell on my side, her shoulder was broken,” he said.

The casualty count was provided by officials in the health and interior ministries.

Kurdish lawmaker Mahmoud Othman blamed the attack on Ansar al-Sunnah, a Sunni Arab insurgent group, and Ansar al-Islam, a mostly Kurdish militant group with ties to al-Qaida in Iraq.

Ansar al-Sunnah claimed responsibility for the last major attack in Irbil — the February 1, 2004 twin suicide blasts at two Kurdish political party receptions that claimed 109 lives.

Othman said authorities had been expecting a major attack somewhere in the Kurdish region since police broke up a militant cell last week in the town of Sulaimaniyah.

“During questioning they confessed they were getting training lessons in a neighbouring country and that was Iran,” he said. “Kurdistan is a safe region and this will have its effect on trade, and companies will fear coming to this region.”

US military officials, who have been saying for months that the Iranians were funnelling funding and training to Shiite militias, have raised recent concerns that Iran is also helping selected Sunni insurgent groups fighting American forces in Iraq.

Maj. Gen. William Caldwell said yesterday that the military had credible intelligence to support the allegation but did not elaborate. He said the support to Sunni insurgents was limited to select groups, which he did not identify.

“We do know that they’re providing support in terms of financial support at this point,” he told reporters.

Most Sunni insurgent groups are strongly anti-Iranian, blaming the Shiite-dominated Iraqi government for helping Iran expand its influence here.

The Irbil attack occurred one day after a suicide car bomber killed 16 people in Kufa, 100 miles south of Baghdad. Those attacks indicated that groups hostile to the government remain capable of launching major strikes across the country while US forces battle to contain violence in the capital.

In Baghdad, a thunderous explosion shook the centre of the capital late in the afternoon, rattling windows of the US Embassy shortly before a press conference by Vice President Dick Cheney.

Cheney’s visit prompted noisy protests by followers of radical Shiite cleric Muqtada al-Sadr, with hundreds taking to the streets in a Shiite area of Baghdad and the Shiite holy cities of Karbala and Najaf.

Protesters burned US flags and demanded that American troops leave.

The US military also announced yesterday that an American soldier was killed and four others were wounded the day before in a shooting attack in the volatile province of Diyala, northeast of Baghdad. The war has now claimed the lives of at least 3,380 US troops.

At least 32 bullet-riddled bodies were found in Iraq on Wednesday, including 21 in Baghdad, most on the predominantly Sunni western side of the Tigris River. They were believed victims of sectarian death squads.

Caldwell reported a “slight uptick” in the numbers of execution-style killings, which had dropped sharply since the start of the security campaign. Caldwell gave no figures.

Shootings and bombings killed at least 40 Iraqis, including Irbil victims as well as nine passengers who were ambushed on a bus travelling from the mainly Shiite city of Diwaniyah to Baghdad.

Gunmen also killed three Iraqi journalists and their driver near the northern oil-rich city of Kirkuk, police said. The four included the director and other employees of the independent Raad media company, which publishes several weekly newspapers and monthly magazines that deal with politics, education and arts.