President Mutharika was reported to have been furious

The three ruling party officials were originally charged on Tuesday with breaching the peace.

But Malawi's attorney-general said there was new evidence of a presidential assassination plot.

Deputy transport minister Roy Cumsay, Harry Thomson and MP Alfred Mwechumu were to meet the president over his anti-corruption drive.

'High-tension meeting'

The BBC's Raphael Tenthani says there has been a growing rift between President Bingu wa Mutharika and governing United Democratic Front (UDF) leaders over his campaign.

These senior people have licences for their guns and how can they plan to kill a UDF-sponsored president? UDF spokesman Salule Masangwi

The talks on 3 January - which were to include former president Bakili Muluzi - were intended to end the rift but was abandoned after the weapons were discovered.

"You don't go to a high-tension meeting where political lives are at stake with guns," Attorney-General Ralph Kasambara told AFP news agency.

A number of large knives had also been found in cars of other UDF officials, he said.

The UDF has reacted angrily to the arrests.

"These senior people have licences for their guns and how can they plan to kill a UDF-sponsored president?" UDF spokesman Salule Masangwi said in a BBC interview.

Since President Mutharika's election last May, several top UDF leaders have been arrested in connection with corruption and fraud scandals.