As British officials debriefed Kussa after his flight to London late Wednesday, the White House also reiterated a senior official's earlier assessment that his decision was a major blow to Qadhafi's government.

National Security Council spokesman Tommy Vietor hailed a "major defection and a significant blow to the Qadhafi regime."

"Mussa Kussa is one of Qadhafi's most trusted aides who can help provide critical intelligence about Qadhafi's current state of mind and military plans.

"It also demonstrates that the people around Qadhafi understand his regime is in disarray."

The Obama administration has argued that it believes that Qadhafi's regime will eventually collapse due to massive pressure exerted by coalition air attacks on his forces, rebel action and a political and economic squeeze.

"The people around Qadhafi have to choose whether to place their bet on a regime that has lost all legitimacy and face grave consequences, or get on the right side of history," Vietor said.

"Mussa Kussa's decision shows which way the wind is blowing in Tripoli."

Mark Toner, a State Department spokesman, told reporters that the British government informed the US authorities about Kussa's defection just before it went public with the development.

But he said Jeffrey Feltman, the assistant secretary of state for Near Eastern affairs, "was not a part of the process to broker his departure and the State Department played no role in these efforts."

Feltman was informed about Kussa's defection by his British counterpart before he departed London on Wednesday, following his attendance at an international conference on Libya, Toner said.

Kussa had been in touch with Feltman recently but "at no point did it come up that he was considering leaving the regime," Toner said.

When asked if Feltman encouraged Kussa to defect, Toner replied that Feltman made clear "our desire to see Qadhafi go and the fact that these individuals, his regime, would be held accountable."

He added: "Yes, in the sense that we made the argument that he was part of a regime that was going nowhere."