Malawi's vice president, Joyce Banda, was sworn in as president Saturday following confirmation that President Bingu wa Mutharika died suddenly on Thursday.

Ms. Banda, who becomes Malawi's first female president, ascended to the presidency as mandated by the national constitution. She took the oath of office in the capital, Lilongwe.

The Malian government officially confirmed Mr. Mutharika's death only early on Saturday, after two days of confusion, rumors and unconfirmed reports about Mr. Mutharika's fate. The delay aroused concerns that a power struggle might be brewing, since Ms. Banda had been expelled by the ruling party two years ago.

President Banda called for calm Saturday, saying the nation will observe 10 days of mourning. She ordered flags on public buildings to be flown at half-staff and said broadcasters should play somber music during the mourning period.

Mr. Mutharika died of a heart attack he suffered at home on Thursday, despite emergency treatment at a hospital in the capital, Lilongwe, after falling ill at home.

He was elected president of Malawi in 2004 and won a second term in 2009.

Mr. Mutharika was credited with improving food security in Malawi and, at one time, making his country a political and economic model for other African countries. In recent years, however, the national economy stumbled and unemployment rose sharply, and critics accused the late president of increasingly autocratic behavior. He suppressed anti-government protests that broke out in July, and 19 people were killed.

An economist by education, Mr. Mutharika was a World Bank official and served as a civil servant in Malawi. He was appointed minister of economic planning and development in 2002, and then-President Bakili Muluzi nominated him as his successor. He later broke away from Mr. Muluzi and formed the Democratic Progressive Party, which has majority control over parliament.