Washington (CNN) -- President Obama is scheduled to meet Monday with his national security team to discuss U.S. strategy in Afghanistan and Pakistan, according to the White House.
The meeting is the sixth in a series of high-level administration discussions being held in part to forge a new consensus on how best to confront Taliban and al Qaeda militants threatening the governments of both countries.
U.S. officials are weighing a reported request from Gen. Stanley McChrystal, the top U.S. commander in Afghanistan, for as many as 40,000 additional troops for the fight against the Taliban.
The meeting is expected to include Vice President Joe Biden via videoconference, Secretary of State Hillary Clinton and Secretary of Defense Robert Gates.
Other expected attendees are national security adviser Gen. James Jones, deputy national security adviser Tom Donilon, White House chief of staff Rahm Emanuel, and John Brennan, assistant to the president for counterterrorism and homeland security.
The strategy review is being conducted against a backdrop of rising U.S. casualties in Afghanistan and political turmoil surrounding a planned November 7 Afghan presidential election runoff.
In Afghanistan on Monday, 14 Americans died in two separate helicopter crashes, NATO's International Security Assistance Force said -- 10 in one incident and four in the other.
It was the largest number of Americans killed in Afghanistan in a single day in at least three years, according to CNN records.
ISAF ruled out enemy fire in the crash that killed four Americans and said that enemy action was not thought be the cause of the other.
Separately, ISAF said a joint international security force killed more than a dozen enemy fighters while searching a compound. The site was thought to harbor insurgents tied to narcotics trafficking in western Afghanistan.
The militants were killed in a firefight when insurgents confronted the joint force, ISAF said.
As the runoff election nears, U.S. military forces are trying to help provide security for the presidential campaign, which is becoming increasingly contentious.
Abdullah Abdullah, the main challenger to Afghan President Hamid Karzai, said Monday that he wants the removal of the country's election chief and 200 other staffers of the election commission to ensure a fair runoff.
Abdullah told reporters that he will submit his conditions to the U.N. Assistance Mission in Afghanistan and the country's Independent Election Commission -- and give them until month's end to comply.
Abdullah has long contended that the head of the Election Commission, Azizullah Lodin, is aligned with Karzai. He has called for Lodin's removal. On Monday, he once again reiterated his demand, saying Lodin has "no credibility."
Abdullah and others have charged that massive fraud occurred in the first round of voting on August 20. The initial results gave Karzai the win, but a subsequent review by a United Nations-backed panel of election monitors threw out nearly one-third of Karzai's votes because of "clear and convincing evidence of fraud."
The result left Karzai short of the 50 percent need to avoid a runoff. After a flurry of meetings with U.S. and U.N. officials, the Afghan president agreed to the November 7 vote.