HARARE, Zimbabwe — President Robert Mugabe, who has ruthlessly ruled Zimbabwe for nearly four decades as one of Africa’s last liberation leaders still in power, was under house arrest on Wednesday, hours after the military announced it had taken him into custody in what appeared to be a coup.

The fate of Mr. Mugabe, 93, who kept a tight grip on his southern African nation despite his increasing frailty and diplomatic isolation from the West, appeared to be in the hands of former allies and opposition officials negotiating his future.

In the capital, Harare, about half a dozen tanks were stationed around strategic government buildings and intersections. But shops and banks were open, and most people carried on business as usual, perhaps because the apparent coup had occurred without violence or resistance. Soldiers blocked the main road leading to the airport, which Mr. Mugabe, 93, had renamed after himself just last week.

The military did not say whether Mr. Mugabe had been removed as president, leaving open the possibility that he may be kept on during a period of transition. But whatever happens to him, it appeared increasingly clear on Wednesday that an era was coming to a close in Africa.