Last month an embattled Pakistani Prime Minister Yousuf Raza Gilani suggested a military coup was in the works.

ISLAMABAD, Pakistan - An increasingly public battle between the military and the civilian government of this nuclear-armed nation escalated yesterday, as the army warned that Prime Minister Yousuf Raza Gilani’s recent criticism of its chief could have grievous consequences, and Gilani fired his defense secretary.

The developments sent Pakistan’s crisis-prone politics into a new tailspin, hardening a standoff that some analysts say could bring down the unpopular government. The turmoil appears likely to distract from efforts to repair relations between the United States and Pakistan, complicating US hopes of securing Pakistani support as it withdraws from neighboring Afghanistan.

The current civilian-military tensions center on an unsigned memo that was delivered to the Pentagon last May, requesting help in halting a potential military coup and curbing the army’s power. The memo infuriated the army, and the Supreme Court is now investigating the document’s origin and whether it was approved by President Asif Ali Zardari. The government has denied any involvement.

But as pressure mounts, the elected government, with Gilani in the lead, has repeatedly lashed out at the army, which is viewed as Pakistan’s most potent force. Last month, Gilani denounced what he called a “state within a state’’ and suggested that a military coup plot was in the works. Two days ago, Gilani told a Chinese newspaper that the army chief, General Ashfaq Kayani, and Lieutenant General Ahmed Shuja Pasha, head of Pakistan’s top spy agency, had acted illegally and violated the constitution by submitting affidavits about the memo case to the court.

Yesterday, Gilani fired his defense secretary, retired Lieutenant General Naeem Khalid Lodhi, accusing him of “gross misconduct and illegal action’’ and of “creating misunderstanding between the state institutions’’ by not following government procedures for submitting the Kayani and Pasha affidavits. Lodhi, considered close to the army, embarrassed Gilani last month by submitting a statement to the Supreme Court saying that the government had no operational control over the army or intelligence services. He was replaced by a civilian loyal to Gilani, local media reported.

Hours earlier, the army had issued a statement denying that the affidavits filed by Kayani and Pasha were improper and pointing out they were submitted through government channels. Gilani’s accusation “has very serious ramifications with potentially grievous consequences for the country,’’ the statement said, without elaborating.

Civilian governments and the army have often acted as dueling power centers throughout Pakistan’s 64-year history, and the military has usually been the victor. There have been several military coups, and no elected government has completed a full term. The weak current government has essentially security policy to the army.

Few here say that the army is gearing up for an outright takeover. But it is widely perceived as disgusted with Zardari and a government tainted by graft allegations and unable to control a free-falling economy. Some political analysts contend the military wants to oust Zardari through constitutional means and has influenced the Supreme Court’s aggressive stance in the so-called Memogate case and other alleged government wrongdoing.

The government has summoned Parliament in hopes it will approve a resolution in support of Gilani and Zardari, while the army chief has called a meeting of his top generals.