The relation between United States and Pakistan showed signs of strain, Thursday, with Islamabad telling the Obama administration to reduce its troops in the country even as it took steps shut down three intelligence liaison centers.

The U.S. efforts to eliminate insurgent sanctuaries suffered a blow, Thursday, when Pakistan told the U.S. to cut down its troops in the country even as it shut down three liaison centers, also known as intelligence fusion cells, in Quetta and Peshawar.

It was a major blow to the U.S. as the liaison centers were the main conduits for the U.S. to share satellite imagery, target data and other intelligence with Pakistan ground forces in conducting operations against militants, including Taliban fighters who slip into Afghanistan to attack U.S. forces and its allies.

Senior U.S. officials said the centers helped U.S. special operations units coordinate operations on both sides of the border and their shutting down would affect U.S. anti-terrorist efforts in the region.

Not surprisingly, Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, flew down, Thursday, to Pakistan for a hastily arranged meeting with Pakistan army chief Gen. Ashfaq Kayani.

Pakistan's action is not going to affect U.S. air operations viz. air strikes carried out by drone aircraft.

Nonetheless, it highlights the growing strain in the relationship between the two countries.

In January this year, the first signs of crack appeared when Pakistan arrested Raymond Davis, a CIA contractor, who shot down two men in Lahore.

Davis was charged with murder, though he said he killed them in self-defense as they attempted to rob him. The Pakistan government said it would have him tried in court. However, in mid-March, U.S. managed to whisk away Davis, triggering violent anti-U.S. protests in several cities.

Subsequently, Pakistan ordered several U.S. special ops trainers to leave the country, an order the U.S. government suspects is in retaliation for the Davis case.

The relation became further strained when on May 2, U.S. helicopters entered Pakistan's airspace without permission and and a team of U.S. Navy SEALS raided Osama bin Laden's secret compound in Abbottabad and killed him following a 40-minute assault. The raid left Pakistan red-faced as the raid took place barely a mile away from a military garrison.

Announcement that bin Laden's body was buried at sea further inflamed anti-U.S. sentiments and deepened the mistrust between the two countries.

The incident led former Pakistan President Pervez Musharraf to say that U.S. intrusion was an act of war.

Certainly, no country has a right to intrude into any other country. Actually, I mean, technically or legally you see it it's an act of war, Musharraf told in a CNN interview.

If U.S. carries out a similar act in the future, Pakistan could resort to military retaliation, Musharraf warned. It could be a serious situation. We must understand that. The world should understand it and President Obama should understand it, he said.