The United States maintained a studied silence on the nature of the attack on its military base in Afghanistan where Vice President Dick Cheney was staying at the time of the incident.

White House Spokesman Tony Snow on Tuesday refused to get into either the details of the attack or speculate if the incident marked the start of the 'Spring Offensive' of the Taliban [ Images ].

"I don't know. I'd refer it to DOD. I think, at this point, people are still investigating what happened. So we don't have a firm answer for you," he said.

The spokesman did not comment whether publicity about the Vice President's trip and his overnight stay at the base prompted the attack.

"I don't know. I don't know. The fact is the Vice President was committed to having a visit with President Karzai. And they were delayed due to weather," Snow remarked.

"It is an isolated attack. An individual who wants to commit an act of violence, is very difficult to stop," Snow maintained.

Meanwhile, State Department Spokesman Sean McCormack described the attack as a designed attempt to kill innocent people.