US Vice-President Dick Cheney has told soldiers at a US base near Tikrit that militants have made Iraq the "central front" in the war on terrorism.
About 10,000 to 12,000 US troops are stationed at Camp Speicher
Mr Cheney paid tribute to the troops and said their extended deployment was vital to the success of the mission.
A joint US-Iraq security "surge" in Baghdad is entering its fourth month but sectarian violence continues and US troops are being killed every day.
The rally ended a two-day visit on a Middle East tour by the vice-president.
In front of a crowd of about 2,000 soldiers at Camp Speicher, Mr Cheney said: "Extremists from inside and outside the country want to stir an endless cycle of violence, and Al-Qaeda is operating and trying to open new fronts."
Mr Cheney said the solution to the conflict in Iraq would be "a political solution" but that basic security was needed first.
He acknowledged the hardship faced by soldiers who have had their deployment extended, but said it was "vital" to the success of the mission.
He also paid tribute to them, noting that top US military commander in Iraq, General David Petraeus, said they were operating in "the most complex and challenging" environment.
The vice-president, one of the main architects in the war that toppled the former Iraqi leader Saddam Hussein, spent the night in Iraq for the first time.
Tikrit, the former home town of Saddam Hussein, is in a mainly Sunni region.
The vice-president moved on to the United Arab Emirates on the second leg of his Middle East tour, which will also take in Saudi Arabia, Jordan and Egypt.
On Wednesday, Mr Cheney met Iraq's political leaders and US army chiefs to discuss security and attempts at political reconciliation.
Mr Cheney said his talks with Prime Minister Nouri Maliki focused on the operation to curb violence in and around Baghdad.
US officials said Mr Cheney wanted faster progress on the fair division of oil revenues and the passage of laws to reinstate former Baath Party officials.
Meanwhile, the Pentagon has told 35,000 US troops they may be required in Iraq this autumn.
President George W Bush has already placed an extra 30,000 troops in Iraq as part of the 12-week-old security "surge" in Baghdad and in the western province of Anbar.
The latest Pentagon order would enable this push to be maintained until the end of the year, if necessary.
However, a defence department spokesman said no decision had yet been taken on prolonging the current surge.
In Washington, the president's Republican party is battling Democrat rivals who want Congress to place checks on funding for the war in Iraq.