Mr Mutharika fell out with his predecessor after becoming president
Heavily armed police in Malawi have arrested four opposition officials and ex-security chiefs after the president said that was a plot to remove him.
Those arrested include a former army commander and police chief.
President Bingu wa Mutharika at the weekend accused his predecessor Bakili Muluzi of being behind a plot to remove him by Friday 16 May.
Mr Muluzi, who is out of the country, and his United Democratic Front (UDF) party have denied the claims.
The BBC's Raphael Tenthani in Blantyre says the homes of former army commander Gen Joseph Chimayo, former Inspector General of Police Joseph Aironi, UDF Secretary General Kennedy Makwangwala and former Blantyre Mayor John Chikakwiya were raided on Tuesday morning.
They were briefly held at the police headquarters in Blantyre before being transferred to the capital, Lilongwe, for interrogation, he says.
Information Minister Patricia Kaliati denied that the arrests were politically motivated.
"They have been arrested as any other citizen would if they break the country's laws," she said.
President Mutharika had been involved in talks with the opposition to try and resolve a political impasse that has seen the opposition either boycotting parliament or shooting down government bills.
But at a church meeting on Sunday the president accused Mr Muluzi of being "a coward" for leaving the country while a coup was being planned.
"Malawians, let me tell you this was their plan: That Bakili Muluzi would come back home [from London] on 16th and that would not be as leader of his party, but that he would come back home as president of Malawi after removing me from power," Mr Mutharika said.
But Mr Muluzi on Monday denied the allegations on his private Joy Radio.
"I am not a violent person," he said.
"I think there is something seriously wrong with our president."
Our correspondent says the arrests have derailed the already troubled parliamentary session where the opposition-dominated parliament is refusing to debate any government bills unless Speaker Louis Chimango expels the more than 70 MPs who defected from the UDF to join President Mutharika's newly founded Democratic Progressive Party (DPP).
Last month, Mr Muluzi, who served two terms before stepping down in 2004, won a contest to be named the UDF's presidential candidate in next year's polls.
It is not clear if he would be eligible to stand as the constitution bans a president from more than two consecutive terms.
President Mutharika was elected as the UDF candidate in 2004 but soon afterwards fell out with Mr Muluzi and formed his own party.