Tanzania's President John Magufuli has warned his new cabinet against the "strange sickness" of leaking confidential official communications on WhatsApp groups.

President Magufuli also warned ministers against taking "selfies" while on duty, saying their work will be "visible" through results achieved.

He made the remarks on Wednesday at an event to swear in ministers and their deputies in the capital, Dodoma.

"In government there is now a strange sickness where even communications are posted on WhatsApp groups. Some confidential communications are being leaked. Let's adhere to our oaths," President Magufuli is quoted as saying in a tweet by the government spokesperson.

Mr Magufuli was re-elected in October in a landslide victory in a poll that the opposition described as fraudulent. The president got 84% of the vote.