Balad-Air-Base (Iraq), Mar 18: The United States intends to complete its mission in Iraq and will not allow the country to become a staging ground for further terrorist attacks on Americans, U.S. Vice President Dick Cheney said on Tuesday.

"All Americans can be certain that we intend to complete the mission so that another generation of Americans does not have to come back here and do it again," Cheney told about 3,000 U.S. troops at Balad Air Base 70 km north of Baghdad.

The war in Iraq, which enters its sixth year this week, is deeply unpopular in the United States and has contributed to President George W. Bush's low popularity ratings. It is a major issue in the U.S. presidential election.

Democratic presidential candidates Hillary Clinton and Barack Obama are campaigning to bring U.S. troops home while the presumptive Republican candidate, John McCain, supports keeping high numbers of troops in Iraq until it is more stable.

Cheney, on a visit to Iraq to assess the success of a U.S. troop build-up, on Monday called the 2003 U.S.-led invasion of Iraq a "successful endeavour" and promised Iraqi Prime Minister Nuri al-Maliki the unwavering support of the United States.

"We have no intention of abandoning our friends or allowing this country ... to become a staging ground for further attacks against Americans," Cheney, an architect of the 2003 invasion, told the soldiers at Balad.

The Bush administration has said that leaving Iraq too soon would undercut security gains and allow al Qaeda militants there to regroup, potentially posing a future threat to the United States.

The vice president spent the night with his wife Lynne in a trailer at Balad, one of the largest U.S. air bases in Iraq. In the early hours there was a barrage of mortar and artillery fire lasting for several hours.

Megan Mitchell, a spokeswoman for Cheney, told reporters travelling with him that U.S. troops on the base had launched pre-emptive fire against areas where they believed "the enemy is located".

Eating a breakfast of egg, sausages and bacon with troops later, Cheney told reporters that no one had told him what the noise was.

"Nobody came running in to wake me up," he said.

Balad Air Base is in the heart of Salahuddin, one of four northern provinces where U.S. and Iraqi forces have staged a series of offensives targeting Sunni Islamist al Qaeda in Iraq.