Top general: Pentagon working to ‘eliminate’ threat of insider attacks

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On NBC’s "Today" show, Allen said that the Taliban recognized "an opportunity to try to split us apart" by infiltrating Afghan security forces to carry out the deadly “blue on green” attacks on NATO troops.

"This has my full attention, we're going to work as hard as we possibly can and around the clock to understand the problem and I think we've got a good grip on it now. and to work very closely with our Afghan partners to eliminate this threat," Allen said. 

Allen warned though that the Taliban would continue to use infiltration and coercion to launch more attacks on Western troops. 

Fifty-one coalition soldiers, a majority of whom are American, have been killed by their counterparts in the Afghan National Security Force (ANSF) and local police this year.

The spike in insider attacks has sparked concern in Washington that the deaths could upset American plans in Afghanistan.

President Obama and Defense Secretary Leon Panetta have pressed Afghan President Hamid Karzai to introduce better vetting measures to keep potential threats out of Afghan units, and in August, Allen ordered American troops to be armed at all times to defend themselves.

But congressional lawmakers have called on the administration to take further steps to protect American lives.

House Homeland Security Committee Chairman Pete King (R-N.Y.) has called the attacks a “growing crisis” and pressed the White House to launch an investigation.

House Armed Services Committee member Rep. Duncan Hunter (R-Calif.) has also written a letter to Chairman Buck McKeon (R-Calif.) asking him to hold further hearings on the issue.

Allen, who is expected to provide a recommendation on troop levels before the end of the calendar year, also said more troops will "probably" return home. However, he said further evaluation of the insurgency and progress training Afghan forces is needed before a recommendation is made. 

The United States intends to hand over responsibility for security to Afghan forces in 2014.

"We really need to look at how the Afghans have come this year, how far they've come," said Allen. 

When pressed on whether special operations forces combat operations would continue in Afghanistan past 2014, Allen said the U.S. intent is to maintain only a "training and advising" role past that date. 

"The war for all intents and purposes ends on the 31st of December, 2014," said Allen.