President Obama considers the death of 24 Pakistani troops in a cross-border fight involving NATO forces a tragedy, the White House said Monday, adding that the administration is determined to look into the circumstances of the weekend air strikes.

The pledge comes as the administration announced Pakistan is considering pulling out of an international conference on Afghanistan next week.

State Department spokesman Mark Toner said Pakistani officials have informed the U.S. they are reviewing their participation. He acknowledged that the weekend incident was a setback for U.S.-Pakistani relations.

White House spokesman Jay Carney said Monday the president extends sympathy to the families of the dead soldiers and to the people of Pakistan in general. 

"We take it very seriously," he said.

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The incident has deepened tensions between the United States and Pakistan, a country that has been essential to the U.S. in its effort to combat al Qaeda and the Taliban. 

Carney called the relationship with Pakistan complicated, but said it is important to maintain a cooperative relationship with Pakistan.

The conference next week in Bonn, Germany, seeks a strategy to stabilize Afghanistan a decade after al Qaeda used the country as a base to launch the Sept. 11 attacks and U.S.-backed forces overthrew the Taliban.

Toner urged Pakistan to attend.

He also said Monday that investigations were under way into the NATO strikes. He said Washington and Islamabad will have to work through the difficulties in their "vitally important" relationship.

The Associated Press contributed to this report.