During his visit to America's other war, Gates is expected to meet President Hamid Karzai, as well as the commander of international forces in Afghanistan, US General David Petraeus, and other officials, his staff said.

Gates said Wednesday that America's war in Iraq is over but that the outcome would remain "clouded" by the reason it was waged in the first place.

Asked by reporters at Camp Ramadi, an American base about 100 kilometres (80 miles) west of Baghdad, whether the United States was still at war in Iraq, Gates replied: "I'd say we're not. Combat operations have ceased.

"We are still going to work with Iraqis on counter-terrorism, we are still doing a lot of training and advising," said Gates, who had arrived early Wednesday on an unannounced visit to Iraq.

"So I would say we've moved into the final phase of our engagement in Iraq," he said, after meeting US soldiers staying on to provide assistance to the Iraqi army.

President Barack Obama late Tuesday officially announced the end of the US combat mission in Iraq, where US forces are now down to around 49,700, for an advisory and training mission -- with the last forces to leave in 2011.

The end of US combat operations in Iraq has shifted attention to America's war in Afghanistan, where troop deaths are at record highs and rampant corruption underscores the challenges facing the West.

As Obama drew a veil over the seven-year conflict in Iraq, the annual death toll of American soldiers in Afghanistan reached its highest point since the war began almost nine years ago.

With momentum increasingly seen to have turned in the Taliban's favor, Obama appeared to step back from an earlier pledge that US forces would begin withdrawing from Afghanistan in July 2011.

"Next August we will begin a transition to Afghan responsibility," Obama said in an address to the nation Tuesday.

"The pace of our troop reductions will be determined by conditions on the ground, and our support for Afghanistan will endure," he said.

"But make no mistake, this transition will begin because open-ended war serves neither our interests nor the Afghan people's."

His words echoed those of the commander of US and NATO forces in Afghanistan, US General David Petraeus, who told AFP in Kabul on Tuesday the withdrawal would be gradual, starting in small secure areas.

US political and military officials have been eager to reassure Afghans that any withdrawal will depend on conditions on the ground and the ability of Afghanistan's own police and army to take on responsibility for security.

The United States and NATO are building up their troop numbers in Afghanistan to almost 150,000, with Obama's surge of an additional 30,000 soldiers almost complete, Petraeus said.