KABUL -- US Democratic presidential hopeful Barack Obama told US media the situation in Afghanistan was critical and it should be the focus of the "war on terror" as he ended a visit to the war-torn nation.

Obama held talks with President Hamid Karzai, whom he has criticized for not doing enough to rebuild Afghanistan, before ending his two-day visit and continuing a major international tour with his next stop expected to be Iraq.

The Illinois senator said in an exclusive interview with CBS in Afghanistan that conditions in the country were "precarious and urgent" and it needed more troops to battle a surge in extremist violence.

"The Afghan government needs to do more, but we have to understand that the situation is precarious and urgent here in Afghanistan," Obama told the broadcaster.

Obama said the United States had been "distracted" by the war in Iraq and should instead be focused on fighting Al-Qaeda in Afghanistan.

"And I believe this has to be our central focus, the central front on our battle against terrorism," he said.

The presumptive presidential nominee for the Democratic party, Obama has made Afghanistan a key part of his foreign policy pledges, promising to send more troops to battle insurgents here if elected.

He has been critical of Karzai's administration, telling CNN this month it had "not gotten out of the bunker and helped to organize Afghanistan and (the) government, the judiciary, police forces, in ways that would give people confidence."

Asked if Obama's comments on Karzai came up at their talks on Sunday, presidential spokesman Homayun Hamidzada said the meeting was friendly and discussions were at a "broad level."

"We didn't see that as criticism because there's a degree of realism in that statement.

"While we're making significant progress in rebuilding our country ... we're spending lots of our resources and energy fighting terrorism that is exported from the south," he said, in a clear reference to Pakistan, where US officials have said extremists have sanctuary.

Obama -- on his first trip to Afghanistan -- and two US senators accompanying him ate breakfast Sunday with American troops at a US military camp in Kabul.

On Saturday, they met senior military commanders at the main American base at Bagram, north of the capital, for a briefing on the international effort to quell the deadly insurgency.

The delegation later flew to a base in eastern Afghanistan, close to the border with Pakistan, where they met Afghan officials and some of the 36,000 US soldiers stationed here.

In a radio address Saturday to coincide with Obama's visit, his Republican rival John McCain criticized the senator for announcing his strategy for Afghanistan and Iraq before his fact-finding tour.

An extremist insurgency was launched in Afghanistan after the Taliban were removed from government in late 2001 in a US-led invasion.

The hardliners were attacked after they refused to hand over Al-Qaeda leaders for the 9/11 attacks that killed around 3,000 people.

The number of international troops in Afghanistan has since risen to nearly 70,000 -- about half of them US nationals.

But the unrest has grown, too, with some of the bloodiest incidents occurring in recent months, including an attack on a remote outpost last month in which nine US soldiers were killed and 15 wounded.

Another international soldier was killed in fighting in eastern Afghanistan on Sunday, NATO's International Security Assistance Force said.

It did not give the nationality of the soldier, though most foreign troops in the east are American.

This year, 137 international soldiers have lost their lives in Afghanistan, most of them in combat.