Bush launched his trip under extraordinary security on Wednesday with a surprise stopover in Afghanistan, his first since the United States led a global campaign to overthrow the militant Taliban regime in 2001 after the September 11, 2001 terror attacks.

The centerpiece of his five-day trip was the clinching of a landmark civilian nuclear deal with India that aimed to firm up the strategic partnership between the world’s most powerful and most populous democracies.

But the "war on terror" kept haunting him during the regional swing.

On Thursday, when he was meeting with Indian Prime Minister Manmohan Singh in New Delhi, an American diplomat and a US consulate employee were killed by a suicide bomber in the southern Pakistani city of Karachi.

A day later, while Bush travelled to the southern Indian city of Hyderabad, where nearly half of the population are Muslim, posters of terror mastermind Osama bin Laden were held up by demonstrators opposed to US foreign policies.

Counterterrorism was a common theme in Bush’s talks with Singh, Pakistani military ruler General Pervez Musharraf and Afghan President Hamid Karzai.

By working with these leaders and their peoples, "we’re seizing the opportunities this new century offers and helping to lay the foundations of peace and prosperity for generations to come," Bush told Americans in a radio address from here before his return home Saturday.

Illustrating the terrorism concerns, Bush arrived in Islamabad late Friday under cover of darkness, with the window blinds of his Air Force One pulled down and the lights off to conceal its presence. He was then taken by a helicopter and billeted at the heavily fortified US embassy.

Bin Laden and his key lieutenants are believed seeking refuge in rugged mountainous tribal areas along Pakistan’s border with Afghanistan. Taliban commanders are also reportedly taking sanctuary in Pakistan.

"There’s a lot of work to be done in defeating AlQaeda," Bush told reporters after talks with Musharraf but added that the Pakistani leader understood the high stakes involved in the battle.

"Part of my mission today was to determine whether or not the president is as committed as he has been in the past to bringing these terrorists to justice, and he is," Bush said, with Musharraf by his side.

In New Delhi, Bush clinched a deal with Singh in which India agreed to place its civilian atomic reactors under global scrutiny for the first time in more than three decades in return for foreign nuclear technology.

The agreement effectively ends India’s status as a nuclear pariah, even though it refused to sign the Nuclear Non-Proliferation Treaty.

India has been under sanctions on transfer of nuclear material or technology since its maiden nuclear weapons test in 1974.

Bush faces an uphill task of convincing a suspicious Congress to give mandatory approval to the deal, which also has to be endorsed by the 45-nation Nuclear Suppliers Group.

"Buffeted by political turmoil at home, President Bush sought a foreign affairs victory in India," said Joseph Cirincione, an American nuclear weapons expert, apparently referring to issues such as the unending violence in Iraq.

Bush, he said, has given in to demands from the Indian nuclear lobby to exempt large portions of the country’s nuclear infrastructure from international inspection.

But the US leader said, "this agreement is good for American security because it will bring India’s civilian nuclear program into the international non-proliferation mainstream."