White House said on Monday that the NATO strikes that killed 24 Pakistani soldiers are a "tragedy, " vowing to carry out investigation on this deadly incident, amid the continuously deteriorating U.S.-Pakistani relations that have been seriously marred by multiple disputes this year.

At a regular briefing, White House spokesman Jay Carney said the U.S. reaction is that "the events that took those lives was a tragedy." The comments came after a total of 24 Pakistani soldiers were killed and 13 others injured when NATO fighter jets and helicopters bombed two border posts in Mohmand tribal region near the Afghan border early Saturday morning.

"We take this matter very seriously," Carney told reporters, vowing that the U.S. will investigate the matter and is "very keen " on finding out what exactly happened.

It is not the first time that Pakistani soldiers became the victims of NATO cross-border attacks. A Pakistani army spokesman said on Monday that a total of 72 Pakistani troops were killed and over 259 others injured in similar attacks over the past three years.

In an angry reaction to the attacks, the Pakistani government on Saturday night decided to close the NATO logistic supply lines in Pakistan with immediate effect and ordered the U.S. to vacate a key airbase in the country's southwest Balochistan province within 15 days.

Pakistani Prime Minister Syed Yusuf Raza Gilani warned on Monday that his country's relationship with the U.S. can only continue with mutual respect and mutual interest.

The U.S.-Pakistani ties have been sent to a decade low by a series of disputes between the two countries, including the U.S. secret raid into Pakistan in May that killed Osama bin Laden and the quarrels on the al-Haqqani networks which is accused by the U. S. as a "veritable arm" of Pakistan's intelligence service.

Pakistan sees the killing of its soldiers and secret raids into the country as a violation of its sovereignty, while the U.S. always complains about insufficient cooperation from Pakistan on its counter-terrorism effort.

At the briefing, Carney described the relationship with Pakistan as "important" but "complicated."

He said it is in America's national security interest to maintain a cooperative relationship with Pakistan because of the shared interests in the fight against terrorism.

"So we will continue to work on that relationship," Carney added.