Concerned about the faltering war in Afghanistan, U.S. President Barack Obama plans to dispatch thousands more military and civilian trainers on top of the 17,000 fresh combat troops he's already ordered, people familiar with the forthcoming plan said Thursday.

Obama, who plans to lay out his revamped strategy for Afghanistan and Pakistan on Friday, also will call for increasing aid to neighboring Pakistan as long as its leaders confront militants in the border region.

Several sources told the Associated Press the strategy includes 20 recommendations for countering a persistent insurgency that spans the two countries' border, including sending 4,000 U.S. trainers to try to increase the size of the Afghan army.

White House press secretary Robert Gibbs would not discuss specifics of the plan, but said Obama is beginning to discuss its findings with members of Congress and others. Obama's top military advisers briefed key lawmakers Thursday.

In broad terms, Obama will define U.S. objectives as eliminating the threat from al-Qaeda to undermine or topple U.S.-backed elected governments or to launch attacks on the United States, its interests and allies, the sources said.

Sources described the recommendations on condition of anonymity because the final wording was not complete. The new plan identified al-Qaeda as the target in a larger network of insurgents who threaten U.S. and allied forces in Afghanistan, often from sanctuaries across the border in Pakistan.

The additional 4,000 troops devoted to training and advising the Afghan armed forces would head to Afghanistan this spring and summer. They come on top of about 17,000 combat and support troops Obama wants in place by the end of the summer.

More than 2,800 Canadian soldiers are serving in Afghanistan.

Democratic Sen. Carl Levin, chairman of the Armed Services Committee, said the training group is needed because there aren't enough U.S. military advisers there now.

"We've got to increase the size [of the Afghan army] much more quickly than contemplated and the trainers are the key to that," said Levin.

Republican Sen. John McCain said it seemed like a viable strategy as long as the manpower is there.

"I know we need more than the 17,000," he said.

The forthcoming White House review also says the U.S. will add hundreds of civilian advisers to those already in Afghanistan. The so-called civilian surge would concentrate on improving life for ordinary Afghans, and would include experts in agriculture in a country where subsistence farming is the norm.

The civilians are also meant to help extend government services and the administration of justice.

The plan notes that the top U.S. general in Afghanistan still wants some 10,000 or 11,000 additional U.S. forces next year, but does not say whether Obama intends to fulfill that request now, sources said.

That decision would come by the end of this year.

The plan also broaches dramatically increasing the size of Afghanistan's security forces. It calls for a study to determine the size of the police and military force capable of securing the country. Several defence officials said that could entail doubling the Afghan security force to almost 400,000. However, the strategy review does not recommend any specific figure.

The Obama strategy document deliberately avoids specific numbers, dollar amounts and timelines "in any domain," a senior defence official said. He said the intent is to set goals and a new direction, with specifics of implementation to be worked out in coming months.

The plan also strongly backs legislation by Democratic Sen. John Kerry and Republican Sen. Richard Lugar that would triple humanitarian aid to $1.5 billion US to Pakistan for five years. The bill had been proposed last year by now U.S. Vice President Joe Biden.

Kerry, who took over for Biden as chair of the U.S. Foreign Relations Committee, said he also supports placing some conditions on military aid to Pakistan. Biden's original bill threatened to cut military funding for Islamabad unless the government did more to fight Taliban forces.

Kerry said he planned to introduce next week an updated version of the measure that would increase slightly the $1.5 billion US figure. He also said the strategy prepared by the administration won't be the final word.

"I'm concerned that we still have work to do to adequately deal with the western portion of Pakistan," he told reporters. "It's still a concern. I think this strategy will help to deal with it, but it's not as complete as it needs to be."