Washington, Nov 29 (IANS): The White House Monday said that the NATO strike that killed 24 Pakistani soldiers was a "tragedy", and vowed to carry out a probe into the incident.

"The events that took those lives was a tragedy," White House spokesman Jay Carney said at a regular press briefing.

The attack took place last Saturday when NATO aircraft bombed two Pakistani border posts in Mohmand tribal region, killing 24 soldiers and injuring 13 others.

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

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

In response, Pakistan has ordered to close the NATO supply lines with immediate effect and asked the US to vacate a key air base in southwest Balochistan province within 15 days.