KABUL - Secretary of State Condoleezza Rice said Thursday she has seen progress in Afghanistan during the past few years, despite a determined Taliban insurgency that has disrupted security and prompted concerns that the NATO-led military campaign is faltering.

And Defense Secretary Robert Gates, seeking more military contributions from NATO members, said he's disappointed that some countries haven't sent combat troops to Afghanistan. But he also said he doesn't think the alliance is at a point of risking failure in the country.

"I don't think that there's a crisis, that there's a risk of failure," Gates said during a news conference in Vilnius, Lithuania, after meeting with NATO defense ministers. He said, however, that strengthening the fighting force there would help speed the defeat of the Taliban militants. "My view is that it represents potentially the opportunity to make further progress faster in Afghanistan if we had more forces there."

Gates noted that despite security setbacks, the country has made gains on the civil side of things, improving the daily lives of Afghans.

Rice made the same point from Afghanistan, saying it's tough to fight militants who have waged a battle for control for many years.

"If you look at the Afghanistan of 2001 and the Afghanistan of now there is a remarkable difference for the better," she said.

Rice said it would be unfair to say the NATO and Afghan government efforts aren't working.

"Can we all expect the security situation will still be difficult -- yes, because Afghanistan has determined enemies who laid waste to this country over a period of a decade," said, adding, "The strategy is one that I believe is having a good effect."

Afghan President Hamid Karzai, standing beside Rice at a news conference, defended his leadership, saying the economy and education systems have improved under his watch and there are more democratic freedoms under a new constitution.

"Afghanistan, if given more attention, would be very, very glad and thankful but it is not right that Afghanistan has been forgotten," said Karzai, who was responding to a recent independent report that said the country is in danger of becoming a failed state.

In a show of unity, the secretary made the trip to Kabul and Kandahar -- a former Taliban stronghold -- with British Foreign Secretary David Miliband so they could get a firsthand look at the front lines of the NATO-led fight as they lead an effort to boost the number of NATO combat forces in the country.

Kandahar was the seat of the Taliban regime that ruled Afghanistan between 1996 and 2001. Taliban insurgents remain active in the surrounding province, which lies in a southern block of the country where the Islamist militia draws its strongest support.

All 26 NATO nations have soldiers in Afghanistan and all agree the mission is their top priority. But the refusal of European allies to send more combat troops is forcing an already stretched U.S. military -- focused on the Iraq war -- to fill the gap, and it is straining the Western alliance.

The U.S. contributes one-third of NATO's 42,000-member International Security Assistance Force mission, making it the largest participant, ahead of Britain with about 7,700 soldiers in Afghanistan. The U.S. has another 12,000 to 13,000 troops there involved in counterterrorism operations.

The high-level U.S.-British visit comes in the bloodiest year in Afghanistan since the U.S.-led toppling of the Taliban in 2001. More than 6,500 people -- mostly insurgents -- died in violence in 2007, according to an Associated Press count of figures provided by local and international officials.

The Taliban and al Qaeda-linked militants have turned to suicide bombings and other tactics that make it more challenging to fight, she said.

"It's not work that's going to be completed overnight," Rice said of the efforts to rebuild the country and fight insurgents at the same time.

Earlier Thursday, Rice said the Afghan government must meet its responsibilities in fighting the Taliban.

"This is a two-way street, and I think everybody has to step back and concern ourselves with the Taliban," she told reporters.

Said Miliband: "We've got responsibilities that we're determined to live up to and obligations that we're determined to live up to and ditto for the Afghan authorities. That's something we want to follow through and at the heart of both our strategies is the belief this has to be done with the Afghan government and in fact led by the Afghan government, with our support."

The stop in Kandahar was a rare side trip outside the Afghan capital by the top U.S. and British diplomats to meet with international forces facing a resurgent Taliban on what was once the movement's home ground.

Rice said the brief unannounced visit was not an attempt to show up European nations that have refused to send fighting troops to Kandahar and other southern regions.

"It's just the rationale of being able to get outside of Kabul and see one of the areas that's been very active," she said.

In London on Wednesday, Gates scolded NATO countries who haven't committed combat troops "willing to fight and die" to defeat a resurgent Taliban.