KIRKUK, Iraq — Bombings and shootings are increasing in northern Iraq as part of a power struggle between Arabs and Kurds. Car bombings in oil-rich Kirkuk grew fivefold last month and hundreds of Kurdish families have left the north's biggest city, Mosul, to escape the violence.

The bloodshed is not nearly on the same scale as Baghdad, where thousands have died in recent months in a wave of sectarian killings and insurgent attacks. In the provinces where Mosul and Kirkuk are located, the toll has risen to several hundred during the summer.

But the violence in the north — a region U.S. official had hoped was getting more stable — underlines the difficulty in keeping all of Iraq's potential hotspots under control.

It also suggests growing strains in another of Iraq's sectarian divides. Baghdad has been suffering from violence between Sunni and Shiite death squads. In the north, the tensions are between Arabs and Kurds, who claim Kirkuk as part of their autonomous zone of Kurdistan to the north.

The violence also has begun to take on the grisly nature of Baghdad's sectarian killings: In recent months, authorities in Kirkuk and Mosul have found bodies dumped in the city, their hands bound with signs that they were tortured before their deaths.

Kirkuk officials have gone so far as to dig a 10-mile trench around the southern and western sectors of the city — where Sunni Arabs are concentrated — to cut off side roads in an attempt to stop car bombs from entering.

Some 2,000 Iraqi soldiers and police launched a sweep through Kirkuk on Friday and Saturday, ordering people off the streets and searching homes for weapons and suspects.

"It makes me feel there's some security in the city," Ashti Mohammed, a Kurdish mother of five, said after her house was searched Saturday. "I always feel terrorized each time my children leave for school. If I hear an explosion, no matter how far away, I'm afraid for them."

The number of car bomb attacks in the city jumped from three in August to 16 in September, according to figures from Kirkuk police. The num-ber of deaths from violence in the city rose from 12 to 42.

Numbers for the rest of Tam-im province, where Kirkuk is the capital, were not available. But Associated Press figures gathered from police reports show a swell of violence, peaking in July when at least 93 died, compared with about 20 a month in the spring.

The attacks are largely blamed on Sunni Arab insurgents targeting Kurds and the Kurdish-dominated police force.

Kirkuk is the center of what many warn could be a major conflict looming in Iraq. The Sunni Arab-led regime of Saddam Hussein moved thousands of Kurds out of the city and brought in Arabs to "arabize" the city and solidify control over its oil wealth. The city's population of about 1 million is thought to be about 40 percent Kurdish and 30 percent Arab, with a substantial population of ethnic Turkomen — though exact figures do not exist.

Since Saddam's fall, Kurds have flooded back to the area, many of them living in camps or stadiums awaiting new homes. The Iraqi constitution calls for Kurds to be assisted in return-ing and for those brought in by Saddam's regime to be removed ahead of a referendum on whether to include the city in the Kurdistan region.

Sheik Abdul-Rahman al-Munshid, a top sheik in the Sunni Arab Obeid tribe, blamed the increasing violence on "the attempts at ethnic cleansing that the Arabs feel Kurdish parties are working for."

"It is the demands of the Kurdish political forces and their attempt to throw out all groups and to work to make Kirkuk part of the northern region that create this fear among non-Kurds," he said.

In Mosul, to the northwest, it's the Kurds who are feeling under siege. Some 750 families have moved out of the city in the past three months, fleeing to Kurdish villages in the province under the protection of Kurdish peshmerga militias, said Hamid Zaimil, a Kurdish representative on the city council.

Abdul-Ghani Botani, an official with the Kurdistan Democratic Party — one of the two chief Kurdish parties — said 1,500 families have fled the city since Saddam's fall in April 2003.

On Saturday, a prominent KDP lawyer was shot to death outside his home. In August, a suicide bomber detonated a car packed with explosives outside the offices of the Patriotic Union of Kurdistan, the other main Kurdish party, killing nine people.

Sunni Arabs dominate Mosul — but not by much, with some 1.8 million out of the province's 4 million people, living alongside a population of some 1.3 million Kurds. The rest are a mixture of Turkoman, Yazidi and other ethnicities. Police could not provide official death figures from the province, but AP reports showed that deaths numbered around 80 a month from July through September, up from a few dozen a month in the spring.

U.S. forces launched a major sweep in Mosul in late 2004 after Sunni insurgents fleeing their stronghold in Fallujah started carrying out attacks in the city. This year, troop levels decreased gradually, and currently stand at 4,000 troops, tasked mainly with training Iraqi forces. Some troops that already had been due to rotate out were moved to Baghdad in August to participate in the sweep there.

Zaimil, the Kurdish city council member, said Mosul could be feeling the fallout from sectarian tensions further south. He said violence increased when Sunni Arabs fleeing violence by Shiite militias in the far southern city of Basra arrived in Mosul.

Botani, the KDP official said Sunni Arabs "still cannot recognize the Kurdish minority in Mosul."

"We have moved from dictatorship in the government to dictatorship in the street. The old regime used to drive out Kurds, and the same thing is happening now, just now it's done in the streets by killings and bombings," he said.