Malawi President Peter Mutharika on Thursday accused the opposition which has rejected the outcome of last month's election of wanting to "overthrow the government by force".
Backers of the opposition Malawi Congress Party (MCP) allege their leader Lazarus Chakwera was robbed of victory in the May 21 election, which an official count showed he lost by just 159,000 votes.
"We have seen the Reverend Lazarus Chakwera... call for violence and a blood bath to plunge this country into chaos," Mutharika said in a national television address.
"The real objective of the Reverend Chakwera is to overthrow the government by violence and force," he added.
Chakwera has rejected the outcome of the presidential election as "daylight robbery" and launched a court battle to have the result annulled on the grounds of fraud.
Earlier on Thursday, the US ambassador to Malawi was forced to hurriedly leave the MCP's headquarters as police fired teargas at protesters.
MCP supporters had gathered in the capital Lilongwe as part of ongoing street protests.
US ambassador Virginia Palmer told AFP she was making a farewell call at the opposition party headquarters.
"Just as we finished the meeting, apparently rocks were thrown and the police responded with teargas," she said.
"There was teargas flying around but my security people came and we proceeded out without incident."
Call for restraint
The US embassy is located next to the MCP building in Lilongwe.
"I just call on all parties in Malawi to exercise restraint and proceed peacefully while the MCP court case is going forward," said Palmer, who is due to leave her Malawi posting shortly.
"This is a peaceful country and a democratic country and we all need to respect these norms."
Eyewitness Jones Chinkhwangwa told AFP: "As the police continued firing (teargas) we saw the US ambassador's vehicle rushing out of the party headquarters."
"She was whisked away in a car with the US flag."
MCP spokesman Eisenhower Mkaka told AFP that police had raided the party headquarters and disrupted several meetings.
"We had to run for our dear lives. The president (of the party) left the premises," he said.
In the ballot count, Mutharika, of the Democratic Progressive Party, was declared the victor with 38.57 percent of the vote, beating Chakwera on 35.41 percent.
On Tuesday, thousands of MCP supporters marched through the city and burst into government offices.
EU deputy chief election observer Mark Stephens has said "there were a lot of mistakes that were made in the tallying" but there was little evidence of tampering.