KABUL, Afghanistan (CNN) -- U.S. President George W. Bush made a surprise visit to Afghanistan on Wednesday, his first to the country where U.S. forces ousted the Taliban following the September 11, 2001 terrorist attacks.

Bush was meeting with Afghan President Hamid Karzai during a five-hour visit to the capital Kabul and Bagram Air Base, the main center for U.S. troops in the country.

A group of low-flying helicopters carried Bush and his entourage from Bagram, where Air Force One landed, to Kabul, where he was received by Karzai.

"Welcome, the president, to Afghanistan," Karzai said as the two leaders paused for photographs on a red carpet.

Bush is expected to hold a news conference with Karzai, preside over a ceremonial ribbon-cutting for the U.S. Embassy and give a pep talk to troops at Bagram before continuing on his announced trip to India and Pakistan.

"This is an opportunity to show our support for a good friend and ally and emerging democracy," White House press secretary Scott McClellan said of the Afghan stop.

"We stand firmly with the people of Afghanistan as they are charting their own future."

The Afghan stopover was not announced officially until Air Force One landed at Bagram.

"There are security precautions that were taken and we are confident in the security precautions that have been taken. One of those was not informing you of the trip until now," McClellan told reporters.

It was Bush's second visit to a war front. His first was a secret trip to have Thanksgiving dinner in 2003 with U.S. troops in Iraq.

This is Bush's first trip to Afghanistan, where a October 2001 U.S. invasion eventually toppled the Taliban regime that had harbored al Qaeda leader Osama bin Laden and allowed terrorist training camps on its soil.

On Tuesday, the director of the U.S. Defense Intelligence Agency said that while Afghanistan had successful national and provincial elections in 2005, the Taliban "remains capable and resilient."

"In 2005, the Taliban and other anti-coalition movement groups increased attacks by 20 percent," Lt. Gen. Michael Maples told the Senate Armed Services Committee.

"We judge that the insurgency appears emboldened by perceived tactical successes and will be active this spring."

India protests
Bush was making the stopover en route to India, where thousands of people chanted anti-U.S. slogans, waved signs and burned American flags in New Delhi to protest the U.S. president's first trip to the nation.

Bush arrives in the world's largest democracy later Wednesday under tight security.

Bush is hoping to sign a critical nuclear accord with New Delhi, a move which is raising political hackles in both nations.

On his trip the U.S. leader is also trying to boost security and economic ties with India, and try to soothe tensions between India and neighboring Pakistan, also a nation with a nuclear capability.

Pakistan is a key U.S. ally in the war on terror, but many in Washington want to see Islamabad make stronger efforts to dismantle terrorist training camps on its soil.

Under the proposed nuclear deal between New Delhi and Washington, the United States would supply nuclear technology and fuel desperately needed by India to fuel its booming but energy-starved economy.

Speaking with the Indian television network Doordarshan, Bush acknowledged the nuclear issue is a tough one for Prime Minister Manmohan Singh.

"Both of us have to convince our respective people in the interest of having a civilian nuclear program that's separate from a military nuclear program," Bush said.

"In India, I understand the politics is going to be difficult. There is still a lot of work to be done, and we just need to continue to come up with an agreement that both of us can live with."

Bush added, "We will keep trying."

India has pledged in return to separate its military and civilian nuclear programs and open up the civilian ones to international inspection.

But some members of the U.S. Congress, who must approve the deal, believe this deal will undermine the international Nuclear Nonproliferation Treaty, which India has refused to sign.

On the other side, some Indian scientists and nuclear industry supporters say the pact will erode their nation's military ambitions.

Singh is eager to ease these fears.

"There has been no erosion of the integrity of our nuclear doctrine either in terms of current or future capabilities," Singh said recently.

Despite the potential political fallout, there is a lot to gain for both sides from such a deal going ahead, analysts have said.

"The essence of this strategic partnership is to provide a countervailing influence to China ... to act as a restraint on the exercise of Chinese power," security analyst Brahma Chellaney told CNN.

There is an economic incentive for Washington, as well. A more buoyant Indian economy fueled by U.S. civilian nuclear technology could be good news for U.S. manufacturers eager to sell into India's booming marketplace.

'Down to the wire'
Given weeks of hectic discussions between U.S. and Indian diplomats and the huge stakes involved for both countries, Bush is warning negotiations on a final nuclear deal will go down to the wire.

"This is not an easy decision for India nor is it an easy decision for the United States, and implementing this agreement will take time and it will take patience from both our countries," Bush said in an interview.

Speaking on Air Force One while traveling to India, U.S. Secretary of State Condoleezza Rice said some sticking points for the deal remained.

"The one thing that is absolutely necessary is that any agreement would assure that once India has decided to put a reactor under safeguard that it remain permanently under safeguard," she said in a report from The Associated Press.

That would prevent India from transferring a reactor from civilian to military status and exempting it from international inspections.

Rice said she was uncertain whether there would be an agreement during Bush's trip but said the success or failure of his visit would not be determined by that.

"We're still working on it," she said. "Obviously it would be an important breakthrough" for the United States and India.