Soon after the Army statement, Prime Minister Yousuf Raza Gilani sacked defence secretary, retired Lieutenant General Naeem Khalid Lodhi, a move that is likely to ratchet up tension with the country's powerful military.

Lodhi, a retired general, is seen as an Army representative within the civilian government, and his ouster is another ominous sign of near-open conflict in a nation that has seen repeated military coups in its six-decade history.

The Prime Minister's office said in a statement that Lodhi was fired for gross misconduct and illegal action which created misunderstanding between state institutions.

The decision comes during intense friction between the civilian government and the powerful military over an unsigned memo that sought U.S. help in reining in Pakistan's generals.

Earlier this week, Prime Minister Yousuf Raza Gilani was quoted as telling a Chinese newspaper that Army chief General Pervez Ashfaq Kayani had violated the Constitution by submitting statements to the Supreme Court about the memo sent to Washington.

The Army statement said Gilani's statement had ''very serious ramifications with potentially grievous consequences for the country.'' It did not elaborate.

The memo sent to Washington had asked for U.S. help in reining in the Army. The memo outraged the Army, and the Supreme Court ordered a probe to establish whether it had been sanctioned by Zardari.

As part of the investigation, Army chief Kayani and the head of the main spy agency, Lt General Ahmed Shuja Pasha, submitted statements to the court in which they suggested the memo was part of a conspiracy against the Army. The sacked defence secretary had submitted the statements to court.

The memo scandal broke three months ago when businessman Mansoor Ijaz, writing in a column in the Financial Times, said a senior Pakistani diplomat had earlier in the year asked that the memo be delivered to the U.S. Defense Department for help in reining in the military.

Ijaz later identified the diplomat as the then Pakistani ambassador to the United States, Husain Haqqani, an ally of Zardari's who was never liked by the military for his strong advocacy of civilian supremacy.

Haqqani denied any connection with the memo but resigned as ambassador.

Pakistan's Supreme Court has set up a judicial commission to investigate the memo.

Although Pakistan is a U.S. ally, their relations are often difficult and anti-U.S. sentiment runs high. Many Pakistanis see a request for U.S. intervention in Pakistan's affairs as disloyal.

Distrust between civilian leaders and the generals has bedeviled the nuclear-armed South Asian country for almost its entire existence, with the military ruling for more than half of its 64-year history after a series of coups.

A senior military official said the latest tension was very serious.

In December, President Asif Ali Zardari flew to Dubai for medical treatment sparking rumours that he had fled the country anticipating a coup.