Soldiers have taken over the headquarters of Zimbabwe's state broadcaster as explosions echoed across the capital Harare, witnesses say, compounding speculation of a military coup against 93-year-old President Robert Mugabe.
However, Isaac Moyo, Zimbabwe's ambassador in South Africa, claimed the government remains "intact".
He also said the situation in the country "has moved to another level" and that he wished to assure the nation Mugabe and his family are safe and their security is "guaranteed".
"We are only targeting criminals around him who are committing crimes that are causing social and economic suffering in the country in order to bring them to justice", the military said in a statement on state television.
The US State Department said it was "closely monitoring" the situation in Zimbabwe and urged all parties to resolve disputes "calmly and peacefully".
"Finance Minister Ignatius Chombo, a leading member of the so-called "G40" faction of the ruling ZANU-PF party led by Mr Mugabe's wife Grace, has been detained by the military, a government source said".
It said Ambassador Harry K. Thomas, Jr. had advised embassy employees to stay home on Wednesday and USA government personnel have been told to work from home due to the "ongoing political uncertainty".
The statement from the ZANU-PF party was released amid worries that the military might be taking action to oust Mugabe.
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Gen. Chiwenga said the army was prepared to act to end purges within Mr Mugabe's Zanu-PF party.
Later Wednesday, ruling the Zimbabwe African National Union Patriotic Front (Zanu-PF) made a series of announcements on Twitter confirming Emmerson Mnangagwa, who was sacked as vice president last week, as interim party leader and de facto president. Mugabe is widely viewed as a political survivor, but the battle to succeed him has turned toxic, and the latest casualty is Mnangagwa.
Zimbabwean soldiers and armoured vehicles have blocked roads to the main government offices, parliament and the courts in central Harare.
President Mugabe has ruled Zimbabwe since the country won independence from Britain in 1980. The veteran of the country's 1970s liberation war was popular with the military and had been seen as a likely successor to Mugabe. "From the direction of his house, we heard about 30 or 40 shots fired over three or four minutes soon after 2:00 am", a resident who lives close to Mugabe's mansion in the suburb of Borrowdale told AFP.
The US embassy has warned its nationals to "shelter" amid uncertainty and wait for further notice, according to its website.
Robert Mugabe has accumulated a net worth of $10 million (£7.5 million) thanks largely to the fortunes reaped from Zimbabwe's diamond deposits.
There are reports that the military in Harare has said: "We are in control".
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