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WASHINGTON (CNN) -- Iraq said two civilians were killed and others were wounded on Thursday by U.S. fighter jets that pummeled Iraq's air defense system for the second consecutive day. The Pentagon said it had no confirmation of casualties.

U.S. aircraft patrolling the northern no-fly zone on Thursday struck two communications sites, two surface-to-air missile systems and an Iraqi radar site near the town of Mosul, U.S. Defense Department spokesman Lt. Col. Steve Campbell said.

The Pentagon said it had no information on casualties, and that damage to Iraqi forces was still being assessed.

"We take every effort to avoid civilian casualties, but (Iraqi President) Saddam Hussein has to take a lot of the blame as long as he continues to violate the no-fly zones and attack our aircraft," Campbell said.

The latest attacks are in line with the Pentagon's more aggressive policy in halting Iraqi flight activity in the no-fly zones, which Baghdad declared illegal after a four-day bombing campaign by U.S. and British planes in December.

Iraq pressures Turkey

Iraqi Deputy Prime Minister Tariq Aziz said in Baghdad Thursday that Iraq would continue to challenge the no-fly zones "no matter what the sacrifices and consequences are."

Aziz also said he would ask the Turkish government during a visit to Ankara next week to end a U.S.-British mandate to use the southern Turkish air base at Incirlik to launch patrols of the northern no-fly zone.

Campbell said there was no damage to U.S. aircraft and no U.S. personnel were injured in Thursday's clashes.

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In the first incident, between about 12:15 p.m. and 12:30 p.m. Iraqi time (4:15 a.m. and 4:30 a.m. EST), a U.S. Air Force F-15E Strike Eagle observed Iraqi anti-aircraft artillery fire and was "illuminated" by an Iraqi radar system near Mosul, the U.S. Defense Department said.

"Acting in self-defense, one F-15E dropped four GBU-12s on an Iraqi surface-to-air missile communications site," a Defense Department statement said. Two other fighter jets then dropped precision-guided bombs on an Iraqi surface-to-air missile system.

In three separate incidents also near Mosul, U.S. fighter aircraft bombed a surface-to-air missile site, an Iraqi radar site and a missile communications site.

Second day of bombing

On Wednesday, U.S. jets attacked Iraq's air defenses in the southern no-fly zone in response to Iraqi MiG-23s and MiG-25s flying into the exclusion area.

Iraq said one person was killed and others were wounded in a U.S. attack in Najaf city in the south Wednesday. A U.S. military spokesman said he could not confirm any civilian casualties in Wednesday's clash.

Iraq said U.S. missiles hit civilian areas in Basra last month, killing 18 people. Washington admitted a missile accidentally hit a civilian area.

The no-fly zones were imposed after the 1991 Gulf War to protect Kurdish enclaves in the north and Shiite Muslims in the south from possible attacks from Baghdad.

Military Affairs Correspondent Jamie McIntyre andReuters contributed to this report.

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