Pakistan's military was on high alert in Kashmir on Monday as its prime minister warned India against carrying out any "false flag" operations in the disputed region after a U.N. vehicle in the Pakistan-held part came under attack.

Pakistan blamed Friday's attack on India, implying it was aimed at embarrassing Islamabad and harming relations with the international community. The two U.N. observers in the vehicle escaped unharmed.

"I am making absolutely clear to the (international) community that if India was to be reckless enough to conduct a false flag operation against Pakistan, it would confront a strong national Pakistani resolve & be given a befitting response at all levels of the threat. Make no mistake," Prime Minister Imran Khan tweeted Sunday.

Pakistan says the attack on the U.N. vehicle was deliberate, as such vehicles are clearly marked and "recognizable even from long distances."

The U.N. confirmed the attack and said it was being investigated.

India has not commented on the attack or responded to Khan's tweets.

The two nuclear-armed nations are bitter rivals which have fought three wars since gaining independence from British rule in 1947, two of them over the Himalayan region of Kashmir. The territory is split between Indian and Pakistani control, and both claim it in its entirety.

The two sides often exchange fire across the heavily guarded Line of Control in Kashmir. Each accuses the other of routinely violating a 2003 cease-fire.