Malawi's President Bingu wa Mutharika has turned to the courts in his deepening feud with his deputy, his lawyer said Wednesday, in a move aimed at finding a way to push her from office.

Mutharika sacked his Vice President Joyce Banda from the ruling Democratic Progressive Party (DPP) in December in the fallout of a battle over the future leadership of the party.

She went on to form her own People's Party but remains in office as the nation's vice president.

Mutharika has now asked a high court if she has "resigned" as vice president by forming her own opposition party, state attorney Allan Ntata told AFP.

He wants the court to decide if "a sitting vice president can become a president of an opposition political party, which subsequently fields candidates against the ruling party in elections."

The court was also asked to consider if a vice president can "work against her own government and constantly fail to attend cabinet meetings and still be considered a legitimate and continuing vice president."

"The word resign is an important question that needs to be sorted out. Our constitution was done in a rush and it does not answer these questions. We want the court to clarify this," Ntata said.

If the court rules that Banda has resigned, Mutharika would be able to appoint a new vice president to serve out the rest of her term.

Mutharika and Banda were elected on a joint ticket in 2009, but their relations soured when the president's brother Peter was endorsed by the DPP as the next presidential candidate.

She has now emerged as one of Mutharika's most vocal critics, and has vowed to remain as vice president until the end of her term in 2014.

Critics accuse Mutharika of wanting to create a political dynasty through his brother. Opposition parties and civic groups say Mutharika has centralised power in his office since his party won a sweeping victory in 2009 elections.

Anti-government protests turned violent in July, when police shot 19 people dead across the country.