The U.S. White House says it's too soon to say whether the Taliban knew that Vice President Dick Cheney was at Bagram Air Base in Afghanistan when a suicide bomber attacked outside the main gates.

At least 23 people died in Tuesday's bombing, which happened at 10 a.m. local time at the base located about 60 kilometres north of the capital of  Kabul.

The Taliban claimed responsibility for the bombing and claimed Cheney, who was in the region on an unannounced visit, had been the target at the Bagram base.

Tony Snow, the White House's press secretary, said it was an isolated attack and not indicative of  Taliban strength.

U.S. Major William Mitchell said Cheney was far from the site of the blast and called the Taliban claim "far-fetched." Cheney was supposed to be in Kabul at the time of the blast, but weather had delayed his departure.

"I heard a loud boom," Cheney told reporters aboard Air Force Two en route to Oman as part of his return to Washington. "The Secret Service came in and told me there had been an attack on the main gate."

Asked if the Taliban were trying to send a message with the attack, Cheney said: "I think they clearly try to find ways to question the authority of the central government."

"Striking at Bagram with a suicide bomber, I suppose, is one way to do that," he said. "But it shouldn't affect our behaviour at all."

A purported Taliban spokesman, Qari Yousef Ahmadi, claimed that the U.S. vice-president was the target of the attack at the base, some 60 kilometres from Kabul.

"We knew that Dick Cheney would be staying inside the base," Ahmadi told AP telephone from an undisclosed location. "The attacker was trying to reach Cheney."

Ahmadi said the attack was carried out by an Afghan called Mullah Abdul Rahim from Logar province.

CTV's Tom Clark told Newsnet from Afghanistan: "The Taliban and their supporters have eyes and ears everywhere. ... So things that are supposed to be top-secret and hush-hush don't always end up that way."

The blast detonated near the first of at least three gated checkpoints that vehicles must pass through before getting access to Bagram.

The sprawling base houses 5,100 U.S. troops and 4,000 other coalition forces and contractors.

"We maintain a high-level of security here at all times. Our security measures were in place and the killer never had access to the base," Lt. Col. James E. Bonner, the base operations commander, told AP. "When he realized he would not be able to get onto the base he attacked the local population."

There were conflicting reports on the death toll. Karzai's office said 23 people were killed, including 20 Afghan workers at the base. NATO's International Security Assistance Force said initial reports were that three people were killed, including a U.S. soldier, an American contractor and a South Korean soldier. U.S. officials indicated they planned to update that death toll.

Associated Press journalists at the scene reported seeing the bodies of at least 12 people carried in black body bags and wooden coffins from near the base into a market area where hundreds of Afghans had gathered to grieve their loved ones.

The vice president had spent the night at the sprawling base, ate breakfast with the troops, and met with Maj. Gen. David Rodriguez, the commander of U.S. troops in Afghanistan.

About two hours after the blast, the vice-president left on a military flight for Kabul to meet with President Hamid Karzai and other officials, then left Afghanistan.

It was not the first explosion apparently targeting a top U.S. official in Afghanistan. In January 2006, a suicide bomber in Uruzgan province detonated a blast during a supposedly secret visit by the U.S. ambassador, killing 10 Afghans.

With files from The Associated Press