Meanwhile, a car bomb and an explosives-laden sewage pump truck struck Iraqi security forces in Baghdad and northern Iraq as at least 17 people were killed in attacks nationwide.
The Iraqi government reiterated its call for Turkey to use diplomacy, and Prime Minister Nouri al-Maliki said he was dispatching a "high-level" political and security team to Ankara to try to defuse.
A statement by his office said the decision was made after al-Maliki met with senior aides to discuss the crisis.
Washington has pressed its NATO ally not to enter Iraq, fearing that unilateral Turkish military action could destabilize the autonomous Kurdish region in the north, which is one of Iraq's few relatively stable areas. The Kurds also are a longtime U.S. ally.
The explosives-laden car was parked near a gas station across the street from an Iraqi army checkpoint on Saadoun Street when it blew up just before noon, police and army officials said.
The officials, who spoke on condition of anonymity because they weren't authorized to release the information, said four civilians and two Iraqi soldiers were killed and 25 people were wounded, including 19 civilians.
It was the latest in a series of car bombings in the capital despite stringent security measures in place as part of U.S.-Iraqi military operations and celebrations marking the end of the Islamic holy month of Ramadan.
In the northern city of Mosul, a suicide bomber driving a sewage pump truck detonated his payload as he approached a police station that had been recently rebuilt after four previous attacks, police said.
The blast caused most of the building to collapse, killing at least four policemen, including the station chief, Capt. Ibrahim Mohammed, and wounding 75 people, police said.
Police spokesman Brig. Gen. Mohammed al-Waqqa said several nearby shops and cars were damaged as well.
Mosul, 225 miles northwest of Baghdad, has seen a rise in violence that many blame in part on an influx of militants who fled the Baghdad security crackdown.
Nobody claimed responsibility for the attacks, but both bombings bore the hallmarks of Sunni insurgents, particularly al Qaeda in Iraq.
In other developments:
The U.S. military announced the arrest of several militants on both sides of the sectarian divide, including one of five extremists who were believed to be behind last week's rocket attack that killed two U.S. soldiers on Camp Victory, the headquarters for American forces in Iraq.
The suspect was detained along with three known associates early Monday by U.S. soldiers, according to a statement. The alleged militants tried to hide in the Agriculture Ministry compound in eastern Baghdad and the soldiers entered the ministry to detain them, the military said.
"We have reason to believe that, through two intelligence-driven operations over the last few days, we now have detained all of the leadership and the key operatives of the indirect fire cell that attacked Victory Base last week," said Brig. Gen. Vincent Brooks, the deputy commander of Baghdad operations.
The statement didn't identify the militants, but the Agriculture Ministry -- which was closed for the holiday on Monday -- is run by Shiites with a heavy influence by the Mahdi Army militia that is loyal to radical cleric Muqtada al-Sadr.