ISLAMABAD, Pakistan — Pakistan's military on Friday ratcheted up tensions with the U.S., rejecting the findings of a Pentagon investigation into the friendly fire deaths of 25 Pakistani soldiers.

The rejection came amid increasing political instability in Pakistan over allegations that the president, Asif Zardari, had in May sought American assistance to avert a military takeover.

Pakistan's army chief, Gen. Ashfaq Kayani, on Friday denied he was plotting a coup and pledged continued support to the country's 4-year-old democracy. He spoke during a tour of forward military posts in the Mohmand tribal region, near the border with eastern Afghanistan, where the Pakistani troops had died in November after coming under fire from U.S. forces.

Kayani's tour also may have been a deliberate snub to the head of the U.S. Central Command, Gen. James Mattis, who had offered to fly into Islamabad to brief his Pakistani counterparts about the Pentagon report.

Pakistan had demanded a personal apology from President Barack Obama for the soldiers' deaths. None was forthcoming after the U.S. investigation blamed the incident on poor coordination between U.S. and Pakistani forces positioned on either side of Afghanistan's eastern border.

It also found that Pakistani troops had fired first at U.S. troops conducting an operation just inside Afghan territory, mistaking them for insurgents.

A spokesman for the Pakistani military, Gen. Athar Abbas, rejected the Pentagon report, saying Pakistani troops opened fire only after coming under attack by American helicopter gunships.

Pakistan's military had declined a U.S. invitation to join the inquiry, alleging the deadly exchange of fire was intentional.

The Pentagon found there was "no intentional effort" to target the Pakistani army units stationed at two posts along the porous border with Afghanistan.

In Mohmand, Kayani sneered at an American offer of compensation for the families of the dead Pakistani soldiers.

"No one can put a price tag on the blood of the martyrs of the nation," he told Pakistani troops.

Kayani also dismissed speculation that he was plotting to overthrow the government.

Fears of a coup mounted Thursday after Yousaf Gilani, the prime minister, said that "conspiracies are being hatched" to overthrow his government and dismiss parliament.

Gilani did not identify the Pakistani army chief and Ahmed Pasha, the director of the military's Inter Services Intelligence Directorate spy agency as the conspirators, but he insinuated as much by reminding "certain individuals" that they worked for the government and were answerable to parliament.

The prime minister's remarks followed discrete consultations with his coalition partners and the opposition leader, Nawaz Sharif.

Sharif's aides joined a meeting on Thursday of parliamentary party leaders, who vowed to uphold the sovereignty of the parliament.

The regional assembly of eastern Punjab province, where Sharif's party is in power, on Friday unanimously adopted a resolution vowing to fight any threat to Pakistan's democracy.

In a direct retort, Kayani said: "The army is fully cognizant of its obligations and responsibilities under the constitution."

He said speculation about a coup was misleading and was being used as a "bogey to divert the focus from the real issues" of national security.