Iraqi officials say bombings have killed more than 20 people in northern Iraq and Baghdad, a sharp increase in violence after an apparent lull. A spokesman for the U.S. military in Iraq says the spike in attacks is not a surprise.

The wave of bombings includes a suicide car bomb attack aimed at a tribal leader near the town of Sinjar, in northwestern Iraq, and still more bombs in Mosul, Baghdad, and elsewhere.

U.S. military spokesman Major General Kevin Bergner says coalition and Iraqi forces are trying to keep the pressure on extremists.

"There has indeed been an increase in violence in the last few days, largely in areas in which al-Qaida in Iraq operates and with al-Qaida in Iraq signatures, as they have sought to ramp up attacks," said General Bergner.

There is speculation that the timing of the attacks could indicate an organized attempt to undermine claims by U.S. forces that they are making progress toward reducing violence and achieving control over wider areas of Iraq.

He also says the increase is similar to the pattern in previous years when extremists mounted more attacks in conjunction with the Muslim holy month of Ramadan.

But he told journalists the number of attacks is down from levels seen last year and roughly in line with the amount of violence in 2005.

Bergner also says Iraqi forces showed growing skill in a raid Tuesday with U.S. troops on the Rustamiyah military academy.

They detained employees accused in connection with the death of the school's former commander and the kidnapping of the current officer in charge, who was subsequently freed.

Meanwhile, news reports and officials say Turkey and Iraq have agreed to allow Turkish forces to pursue Kurdish separatists into Iraq. The deal was reportedly made during a visit by Iraqi Interior Minister Jawad al-Bolani to Ankara and is supposed to be signed Thursday.

A Turkish television report says the agreement allows Turkey to carry out small-scale military operations against Kurdish rebels in northern Iraq with Baghdad's prior permission.

Turkey says in recent months rebels of the Kurdistan Workers Party have stepped up attacks on Turkish targets from their remote mountain bases in northern Iraq.

Kurdish separatists have been fighting for autonomy in southeastern Turkey since 1984. More than 30,000 people have been killed in the conflict.