BAGHDAD (AP) -- Sen. John McCain stressed the importance of a U.S. commitment to Iraq during talks with Iraq's prime minister Monday, and explosions struck Baghdad during twin visits by the presumptive Republican presidential nominee and Vice President Dick Cheney.
Helicopter gunships circled over central Baghdad and the heavily fortified Green Zone, but no details were immediately available on the cause of the explosions.
McCain, who has linked his political future to U.S. military success in Iraq, met Monday with Prime Minister Nouri al-Maliki shortly before the Iraqi leader began separate talks with Cheney.
Al-Maliki said he and the vice president discussed ongoing negotiations over a long-term security agreement between the two countries that would replace the U.N. mandate for foreign troops set to expire at the end of the year.
"This visit is very important. It is about the nature of the relations between the two countries, the future of those relations and the agreement in this respect," the prime minister told reporters. "We also discussed the security in Iraq, the development of the economy and reconstruction and terrorism."
McCain also said it was important to maintain the U.S. commitment in Iraq and warned that a U.S.-Iraqi military operation to clear al-Qaida from its last urban stronghold of Mosul, 225 miles northwest of Baghdad, will be "very difficult and very important."
McCain, who arrived in Iraq on Sunday, told reporters that he also discussed with the Shiite leader the need for progress on political reforms, including laws on holding provincial elections and the equitable distribution of Iraq's oil riches.
The Arizona senator said he had reviewed the security situation in Baghdad with Iraqi officials.
He also visited the Anbar province city of Haditha on Sunday, drinking soft drinks from street vendors and answering questions about the U.S. presidential campaign to tout recent security gains ahead of the fifth anniversary of the U.S.-led invasion.
Asked by one of the vendors if he would return to Iraq, McCain responded, "We'll come back if I win." Footage of the visit was distributed on a military Web site.
Cheney landed at Baghdad International Airport, then flew by helicopter for talks with U.S. and Iraqi officials. It is Cheney's third vice presidential trip to Iraq where 160,000 American troops are deployed and the U.S. death toll is nearing 4,000.
The U.S. Embassy in Baghdad said it could not confirm reports of a rocket attack on the Green Zone after Cheney's arrival. "I'm not aware of any," embassy spokeswoman Mirembe Nantongo said.
Violence has dropped throughout the capital with an influx of some 30,000 additional U.S. soldiers as well as a Sunni revolt against al-Qaida and a cease-fire by radical Shiite cleric Muqtada al-Sadr's Mahdi Army militia. The U.S. military has said attacks have fallen by about 60 percent since last February.
McCain met with Deputy Prime Minister Barham Saleh on Sunday and planned to meet with Gen. David Petraeus, the top U.S. commander in Iraq, the U.S. Embassy said. Further details of the visit were not released for security reasons, the embassy said.
Before leaving the United States, McCain, who was making his eighth trip to Iraq, said the tour to the Middle East and Europe was for fact-finding purposes, not a campaign photo opportunity.
McCain, the senior Republican on the Senate Armed Services Committee, was accompanied by Sens. Joe Lieberman, an independent, and Republican Lindsey Graham, two top supporters of his presidential ambitions. The weeklong trip will take McCain to Israel, Britain and France.
In other violence Monday, police said they found the bodies of three members of a U.S.-allied group fighting al-Qaida in Udaim, 70 miles north of Baghdad. Members of the mostly Sunni groups have been increasingly targeted by suspected al-Qaida members seeking to derail the recent security gains.
A roadside bomb targeting a U.S. convoy injured four civilians in Baghdad, while a separate bombing in the capital's Mansour neighborhood injured a policeman. Both were reported by police officials on condition of anonymity because they were not authorized to release the information.
Associated Press writers Bushra Juhi and Sinan Salaheddin contributed to this report.
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