President Hamid Karzai on Thursday said he wanted to "correct" rather than damage US-Afghan relations, after a storm of protest over his recent anti-US remarks.

Karzai, who on Sunday suggested that the US was working in concert with Taliban militants, acknowledged there were serious bilateral strains as the NATO-led military coalition starts to withdraw from Afghanistan.

"The president called the United States a friend and strategic partner of Afghanistan and said his recent comments... had been to correct rather than damage this relationship," a statement from his office said.

"The president said that both countries are in a critical stage of relations, therefore it is natural that each side tries to stand for and focus on its national interests."

Karzai told a debate forum held at his palace in Kabul that among the causes of tension were a dispute over Afghan detainees held by the US and civilian casualties in NATO military operations.

"We want a good relationship with America, we want friendship, but friendship between two sovereign nations," Karzai told the audience of invited guests and government officials.

Karzai's allegation of collusion provoked fury among US officials, as both nations negotiate the framework that could allow some American troops to remain in Afghanistan when NATO combat troops leave next year.

The coalition commander in Afghanistan, US General Joseph Dunford, on Wednesday sent an advisory to his senior officers warning that troops faced an increased threat of attack after anti-US comments by Karzai.

"Karzai's remarks could be a catalyst for some to lash out against our forces -- he may also issue orders that put our forces at risk," Dunford said in the advisory, which was obtained by The New York Times.

The president has recently banned international troops from university campuses due to unproven claims of harassment of students.

Last month he also ordered US special forces out of Wardak, a strategic province adjacent to Kabul, and stopped Afghan forces from calling in US air strikes.

"We're at a rough point in the relationship," Dunford said. "(Militants) are also watching and will look for a way to exploit the situation -- they have already ramped up for the spring."

NATO is training Afghan soldiers and police to take over the fight against the Taliban as 100,000 international troops prepare to head home by the end of 2014.

Karzai's recent outbursts have triggered criticism from rival politicians, who say he is deliberately misleading ordinary Afghans and could threaten the future of international aid on which the country relies.

"He says the Taliban and Americans are one," Abdullah Abdullah, a former presidential candidate, said in a speech on Thursday.

"Our people are worried about whether Karzai is right -- or they ask whether it is another conspiracy."

The president's anti-US rhetoric has been widely seen as an attempt to establish himself as a strong nationalist leader before he steps down at the end of his second term next year.