Bush, speaking on Wednesday at a news conference during a visit to Denmark, said Prime Minister Anders Fogh Rasmussen raised concerns about the US detention camp in Cuba.
"The prisoners are well-treated in Guantanamo. There's total transparency. The International Red Cross can inspect anytime, any day," Bush said.
"These people are being treated humanely. There are very few prison systems around the world that have seen such scrutiny as this one," he said.
The Guantanamo camp, where some detainees have been held for three years without being charged, is a sore point in US-European relations.
Even the Danish government, a staunch US ally in Iraq and Afghanistan, has called on the United States to try the Guantanamo prisoners or release them.
Bush noted that many prisoners had been sent home, while the US judicial system is deciding whether to try others in military or civilian courts.
"The reason why you haven't seen any adjudication of individuals is because our court system is determining where best to try people," he said. "Once the judicial branch of government makes its decision, then we'll proceed forward giving people fair and open trials."
About 540 detainees, most of them captured during battles in Afghanistan, are being held at the Guantanamo camp.
The US government contends the prisoners are enemy combatants and are not entitled to constitutional protections.
Rights groups and the ICRC
report abuse cases at the base
However, human rights groups as well as the International Committee of the Red Cross have reported cases of prisoner abuse that amounted to torture at the military base.
In June 2004, an ICRC team that included humanitarian workers and experienced medical personnel found a system devised to break the will of prisoners through "humiliating acts, solitary confinement, temperature extremes, use of forced positions". Ex-prisoners have reported incidents of abuse at the hands of the US military forces.
Bush also issued a message to African leaders on Wednesday, saying they should not expect American aid unless they make efforts to fight corruption.
The US president said helping Africa overcome poverty and disease is a top priority but added he expects "good governance" from leaders on the continent.
"I don't know how we can look our taxpayers in the eye and say it's a good deal to give money to countries that are corrupt"
"We've said that we'll give aid, absolutely, we'll cancel debt, you bet, but we want to make sure that the governments invest in their people," Bush said.
"We expect there to be good governance on the continent of Africa. I don't know how we can look our taxpayers in the eye and say it's a good deal to give money to countries
that are corrupt."
Bush also said the United States must move away from fossil fuels and predicted a rise in hydrogen-powered cars.
He repeated his objections to the Kyoto treaty on climate change and suggested development of new technologies to cut down on heat-trapping greenhouse gases.
The US has not ratified the Kyoto
Protocol for emissions reduction
"There's no doubt in my mind we'll be driving a different type of automobile within a reasonable period of time - one powered by hydrogen," he said.
Bush said he would share strategies for developing alternatives to fossil fuels with G8 leaders.
However, Bush acknowledged that global warming was a problem and said "the US needs to diversify from fossil fuels".
"I recognise that the surface of the Earth is warmer and that an increase in greenhouse gases is contributing to the problem," Bush said.
Protesters in Denmark set the
US flag alight
Bush's visit, his first to Denmark but his fifth meeting with Rasmussen since 2002, was seen by commentators as a symbolic gesture thanking Denmark for supporting the war in Iraq, where it has deployed more than 500 troops near the southern city of Basra.
But while Rasmussen is one of Washington's most loyal allies, the Danish public opposes the war and has harshly criticised Washington's treatment of detainees at Guantanamo and in Iraqi prisons.
Demonstrations against the US leader began on Tuesday afternoon and were scheduled to last until after he leaves Denmark on Wednesday, with some protesters going so far as to burn a US flag and a doll resembling Bush.