US President Barack Obama hasn't heard the "magic phrase" needed to make a final decision from the ongoing review on the Afghan strategy, the White House said on Wednesday. 

White House spokesman Robert Gibbs also told reporters at a press briefing that Obama hasn't decided on the key issue of how much additional forces should be sent to Afghanistan, denying a BBC report which said Obama would approve sending 45,000 more troops to that country.

But he said the bottom line is that withdrawing troops from Afghanistan is not an option.

"The president has been clear to say, we're not leaving Afghanistan," Gibbs noted.

Earlier in the day, Obama held a three-hour session on Afghanistan with his national security teams, but is still not ready to make decisions on strategy and troops.

Five such meetings have been held and another meeting is scheduled for next week.

According to Gibbs, Wednesday's session focused on efforts by the United States and its allies to strengthen the "civilian mission within Afghanistan."

Obama also received an updated report on programs to train Afghan forces.

The meeting in the White House Situation Room was attended by Defense Secretary Robert Gates, National Security Adviser Jim Jones, Chairman of the Joint Chiefs Mike Mullen and others.

Secretary of State Hillary Clinton, who was traveling in Russia, took part by telephone from her plane.

US ambassadors in Afghanistan and Pakistan, Karl Eikenberry and Anne Patterson, as well as top military commander in Afghanistan Stanley McChrystal, also took part in the session by video-link.

The White House has said that a final decision on the Afghan strategy, including troop levels, is still weeks away.