The State Department announced Sunday that it is investigating whether Pakistan made use of one of their U.S.-built fighter jets to shoot down an Indian warplane last week, raising concerns that the neighboring countries were inching towards the brink of all-out war.

The Pakistani government released a captured Indian pilot Friday in an effort to de-escalate recent hostile relations between the two nuclear-capable nations. But, if one of the American F-16 aircrafts was used against India by Pakistan, the move would be in violation of the international arms agreements between the U.S. and Pakistan.

The U.S. Embassy in Pakistan addressed the investigation in a statement Sunday. “We are aware of these reports and are seeking more information,” a embassy spokesperson said. “We take all allegations of misuse of defense articles very seriously.”

“The U.S. Government does not comment on or confirm pending investigations of this nature,” the embassy added.

Pakistani armed forces have vehemently denied using any of the American-built fighter jets in the showdown between Pakistan and India. They have not, however, disclosed what kind of jet was used.

Pakistan remains a top buyer of U.S. weapons and defense systems. The relationship between the nations ramped up following the Sept. 11 attacks when the Bush administration deemed Pakistan a critical ally in the fight against terrorism.