Pakistan's coup leader accused the government of the ousted Mr Nawaz Sharif of "imperilling" a commercial passenger flight in a desperate bid to keep him out of the country.
The army chief, Gen. Pervez Musharraf, told the nation in a televised address that he was returning from an official visit to Sri Lanka when his Pakistan International Airlines (PIA) flight was ordered to "anywhere outside Pakistan".
"On my way back the PIA commercial flight was not allowed to land at Karachi but was ordered to be diverted to anywhere outside Pakistan, despite acute shortage of fuel, imperilling the lives of all the passengers," he said.
"Thanks be to Allah this evil design was thwarted through speedy army action."
Gen. Musharraf told the nation the situation was under control and appealed for its support. "Dear brothers and sisters, your armed forces have never and shall never let you down," he said.
"We shall preserve the integrity, sovereignty of our country to the last drop of our blood. I request you all to remain calm and support your armed forces in the reestablishment of order to pave the way for a prosperous future for Pakistan."
He said the coup was necessary to restore stability to the country, which is reeling from a deep economic recession, internal religious strife and tensions with neighbour India over the disputed region of Kashmir.
The general is a former army commando and artillery officer who took over as Pakistan's army chief a year ago.
Gen. Musharraf (58) became the 12th chief of the country's powerful army following the resignation of General Jahangir Karamat in October 1998.
Gen. Musharraf has been at odds with the prime minister since then.
A graduate of Pakistan's prestigious Command and Staff College in Quetta, Baluchistan, he was commissioned in 1964 in an artillery regiment and fought in the 1965 conflict with India.
Mr Sharif two weeks ago extended Gen. Musharraf's tenure as army chief and chairman of the Joint Chiefs of Staff Committee (JCSC) for another two years, until October 2001.
The extension irked the naval chief, Admiral Fasih Bokhari, who was in line for the post of JCSC chairman on the basis of seniority, and he resigned a few days later.
A government statement at the time said the extension of Gen. Musharraf's term was meant to quash speculation "once and for all" about a change of command in the army.