BAGHDAD, Iraq – A woman disguised in a man’s robes and headdress slipped into a line of army recruits yesterday and detonated explosives strapped to her body, killing at least six recruits and wounding 35 – the first known suicide attack by a woman in Iraq’s insurgency.

The attack in Tal Afar near the Syrian border appeared aimed at showing that terrorists could still strike in a town where American and Iraqi offensives drove out insurgents only two weeks ago. A female suicide bomber may have been chosen because she could get through checkpoints – at which women are rarely searched – then don her disguise to join the line of men, Iraqi officials said.

Iraq’s most notorious insurgent group, Al Qaeda in Iraq, claimed responsibility for the attack in an Internet statement, saying it was carried out by a “blessed sister.”

The bombing came a day after American and Iraqi officials announced their forces killed the second-in-command of Al Qaeda in Iraq, Abdullah Abu Azzam, in a raid in Baghdad over the weekend. His death has not slowed insurgent violence, with at least 84 people – including seven American service members – killed in attacks since Sunday.

President Bush warned violence will increase in the days leading up to a key October 15 referendum on a new constitution, a document that has sharply divided Iraq’s Shiite Muslim majority and the Sunni minority that forms the backbone of the insurgency.

“We can expect they’ll do everything in their power to try to stop the march of freedom,” Mr. Bush said. “And our troops are ready for it.”

The American military announced yesterday that two more American soldiers and an airman were killed in violence and a Marine was killed by a noncombat gunshot.

In the holy city of Najaf, south of Baghdad, an attacker set off an explosion in the home of a bodyguard of radical Shiite cleric Moqtada al-Sadr yesterday, killing two people and wounding five, al-Sadr aides and a hospital official said.

In the attack at the Tal Afar army recruitment center, the female suicide bomber was wearing a traditional white “dishdasha” robe and a checkered kaffiya headscarf – both worn only by men – to blend in with the line of Iraqi applicants, Major Jamil Mohammed Saleh said.

She detonated explosives packed with metal balls and hidden under her clothes, Major Saleh said. Six recruits were killed and 35 wounded, said hospital officials in Tal Afar, 260 miles northwest of Baghdad.

In a photo of the attacker’s head taken by Mr. Saleh, the woman appeared to be in her early 20s with dark eyes, light skin and brownish hair. Major Saleh said it was not known whether she was Iraqi.