BAGHDAD — Gunmen hiding in reeds in a Sunni town south of Baghdad killed seven Shiite pilgrims Sunday as they were marching to a shrine in the capital for a major holiday, officials said.

The young men were ambushed when the attackers opened fire in Madain, about 14 miles southeast of Baghdad, as they were on their way to the shrine in the Baghdad neighborhood of Kazimiyah, a police officer said.

The slain men had begun their trek farther south in the Shiite town of Suwayrah, according to the officer, who is based in Baghdad and read the report about the attack. An official at the Baghdad hospital where the bodies were taken confirmed the killings, but both spoke on condition of anonymity because they were not authorized to release the information.

The area where the attack occurred is a former al-Qaida in Iraq stronghold that has seen a steep drop in violence after local Sunnis joined forces with the Americans against the terror network. Members of so-called awakening councils now patrol the streets of Madain and other cities in Baghdad's southern belts.

Authorities also have tightened security measures as tens of thousands of people are expected to converge on Kazimiyah to mark the death of an 8th century Shiite saint buried in the golden domed shrine there.

Iraqi military spokesman Brig. Gen. Qassim al-Moussawi told The Associated Press that 100,000 members of the Iraqi security forces along with U.S. reinforcements are deployed in Baghdad, and U.S.-led forces will provide air support.

A vehicle ban also has been imposed in Kazimiyah until after the pilgrimage culminates on Tuesday, al-Moussawi said.

Shiite pilgrims have frequently been targeted by insurgents since the U.S.-led war began in March 2003, and the attack underscored the persistence of the insurgents despite recent security gains.

In a bid to tighten the noose on al-Qaida in its last stronghold in northern Iraq, a top U.S. commander said American and Iraqi forces will launch two new operations early next month aimed at routing insurgents from their rural safehavens.

Maj. Gen. Mark Hertling, who commands U.S. forces in northern Iraq, said the Iraqi army will lead a new offensive in Diyala province, while his troops will focus on remote areas throughout the north in a bid to build on recent security gains in northern cities like Mosul and Baqouba.

The purpose of the offensives — dubbed "Omens of Prosperity" and "Iron Pursuit," respectively — is to build on security gains in urban areas of the north, Hertling said.

"We have secured the key cities of the north. We have seen al-Qaida continue to be pushed into what we call the support zones, the areas of the desert," he said. "We will continue to pursue them as they continue to try and find safehavens in the deserts, in the hills and in the palm groves."

Similar efforts against Shiite militiamen in Baghdad and southern cities have contributed to a sharp decline in attacks. But violence has been slower to decline in northern Iraq despite numerous military operations in Diyala and elsewhere in recent years.

Hertling said the U.S. and Iraqi military will flood the area with soldiers and he expressed optimism that much improved Iraqi security forces will succeed where past efforts have failed.

"I think the increase in the number of Iraqi police and Iraqi security forces will contribute to this," he added.

Violence has been reduced by 75 percent across northern Iraq and the Diyala province cities of Baqouba and Muqdadiyah are relatively peaceful, Hertling said, without being more specific.

But he acknowledged the threat from al-Qaida in Iraq and insurgents remains strong as they retain the ability to wage attacks, with suicide bombings in Diyala and car bombs throughout the north.

"There are very many hiding places in the rural areas and those are the areas that now the Iraqi security forces have to go after," he said.

Associated Press writers Bushra Juhi and Qassim Abdul-Zahra contributed to this report.