Ivory poachers have killed more than 80 elephants in Zimbabwe by poisoning watering holes with cyanide, a minister said.
Members of Zimbabwe's opposition say they have been targeted by Mugabe supporters following the president's re-election.
President Robert Mugabe's declaration as winner has been met by international concern over the conduct of the African nation's poll.
Zimbabwean President Robert Mugabe has been sworn in for a new five-year term in the face of criticism from opponents and the West that the election he won in July was deeply flawed.
Mugabe, who has ruled since independence from Britain in 1980, has told critics of his re-election to "go hang" and has vowed to press ahead with nationalist policies forcing foreign firms to turn over majority stakes to black Zimbabweans.
Britain has called for an independent investigation of alleged vote-rigging in Zimbabwe as Robert Mugabe prepared to be signed in for a seventh term as president.
Mugabe's victory in July's poll was declared free and fair by the country's top court despite what Foreign Secretary William Hague described as "strong evidence" of illegality.
"I strongly believe that an independent investigation of any allegations of election irregularities would be required for the election result to be deemed credible," he said in a statement.
"I have grave concerns over the conduct of the election, and the flaws highlighted in the South African Development Community (SADC) and African Union (AU) observation missions' initial assessments."
Zimbabwe's MDC party has withdrew a court challenge against Mugabe's re-election, a party spokesman told Reuters.
Zimbabwean President Robert Mugabe has launched an attack on critics of his disputed re-election, telling them bluntly to "go hang".
In his first public address since his election win, Mr Mugabe dismissed his rivals as "Western-sponsored stooges" at a liberation war commemoration.
The leader of Zimbabwe's Movement for Democratic Change party and Mr Mugabe's main rival, Morgan Tsvangirai, boycotted the rally as allegations of election fraud continued.
Zimbabwean President Robert Mugabe told critics of his disputed re-election to "go hang" dismissing his rivals as "Western-sponsored stooges" at a liberation war commemoration that was boycotted by his principal challenger, Morgan Tsvangirai.
Speaking in the local Shona language, in colloquial phrases he does not usually use when speaking in English, Mugabe called on Tsvangirai to accept defeat:
"Those who are smarting from defeat can commit suicide if they so wish. But I tell them even dogs will not sniff at their flesh if they choose to die that way," he said.
He described Tsvangirai as the "enemy" in his party's midst during the shaky coalition brokered by regional leaders after the last disputed and violent poll in 2008.
"We have thrown the enemy away like garbage. They say we have rigged, but they are thieves"
Zimbabwe's MDC party has filed papers in the Constitutional Court challenging Robert Mugabe's election win.
My lawyers are at court filing papers challenging validity of July 31 poll
Botswana's government has disputed the result of Zimbabwe's general election which saw the long-standing president Robert Mugabe claim a landslide victory.
Its assessment stands in stark contrast with that of South Africa, which has congratulated Mr Mugabe on his victory.
Both nations belong to the Southern African Development Community which monitored the vote, and now appears to be divided.
The Botswana government said that although the election day itself had been "free of overt intimidation and violence", the electoral process "cannot be considered as an acceptable standard for free and fair elections".
Zimbabwe's main stock market index fell 11 percent on Monday in its first trading day since official results confirmed President Robert Mugabe would extend his 33 years in power.
The industrial index fell to 205.57 points in the mid-morning session, with all the top-ten shares save for the local unit of insurance giant Old Mutual trading in the red.
Young Zanu-PF supporters from the Mbare area of Harare, Zimbabwe have been celebrating in the streets following Robert Mugabe's victory in the country's presidential election.