Britain today urged all sides in Zimbabwe to refrain from violence after the military took control of the country, but said it was "potentially a moment of hope".
"We have all seen what has been taking place in Harare. We are monitoring those developments very carefully," Prime Minister Theresa May told MPs.
"The situation is still fluid, and we would urge restraint on all sides because we want to see and we would call for an avoidance of violence."
She said the primary concern of Britain, the formal colonial power, was for the safety of about 20,000 of its nationals who live in Zimbabwe.
The government changed its travel advice today, urging Britons in Harare "to remain safely at home or in their accommodation until the situation becomes clearer".
Zimbabwe's military is in control of the country and President Robert Mugabe, in a conversation reported by South African President Jacob Zuma, has said he is under house arrest. But generals have denied staging a coup.
Answering an urgent question on the situation in the House of Commons, Foreign Secretary Boris Johnson urged caution in predicting how the situation will unfold.
"We do not know whether this marks the downfall of Mugabe or not, and we call for calm and restraint," he said.
But he added: "I think this is potentially a moment of hope. Lots of people in this country will be looking at it in that sense.
"We must make sure we don't jump the gun, that we aren't premature, and that's why I've been cautious with the House today."
Johnson said he would be talking to the deputy president of South Africa later today about the response of the international community.
He said he is also going to a European Union and African Union (AU) summit later this month, where Zimbabwe was now likely to be a priority.
"All Britain has ever wanted for Zimbabweans is to be able to decide their own future in free and fair elections," he said.
"Mugabe's consuming ambition was always to deny them this right.
"Britain has always wanted the Zimbabwean people to be masters of their fate and for any political change to be peaceful, lawful and constitutional."
Mugabe was once heralded as a liberator who rid the former British colony Rhodesia of white minority rule, but was soon cast in the role of a despot who crushed political dissent and ruined the economy.
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