Uganda's military chief said on Friday that authorities had detained 2 000 opposition supporters, killed 30 and were hunting for more following a disputed presidential election in which his father Yoweri Museveni, won a seventh term.

Museveni, 81, who has led the East African nation for nearly four decades, was declared to have resoundingly defeated Bobi Wine, leader of the opposition National Unity Platform (NUP) party in the January 15 vote, held during an internet blackout.

Wine, a former musician whose legal name is Robert Kyagulanyi, rejected the election result, alleging widespread irregularities including ballot stuffing, and went into hiding.

In a series of overnight social media posts, military chief Muhoozi Kainerugaba, Museveni's son, gave the first details of the arrests and killings of NUP supporters, describing them as hooligans and terrorists.

"So far we have killed 30 NUP terrorists," Kainerugaba said on X, without explaining the circumstances of the deaths. "Most NUP terrorist leaders are in hiding. We shall get them all," he said in another post.

The government has accused Wine's supporters of violence during the election while the opposition says its members were attacked by security forces. Reuters has not been able to authenticate the allegations.

A police spokesperson declined to give any further comment on the situation. Military spokesperson Chris Magezi could not be reached for comment.

Reacting to the situation in Uganda after the election, United Nations Secretary-General Antonio Guterres expressed concern over the arrests and violent incidents involving opposition figures and supporters, spokesperson Stephane Dujarric said late on Thursday.

"He (the Secretary General) notes the importance of restraint by all actors and respect for the rule of law and Uganda's international human rights obligations," Dujarric said.

Wine has alleged that hundreds of his supporters have been illegally detained in recent months, targeted for their political affiliation and said this was aimed at instilling fear and intimidating his supporters.

Uganda's opposition parties and rights activists say some of those arrested are held in unofficial detention centres where some are tortured.

The crackdown has intensified with the recent detention of Muwanga Kivumbu, a lawmaker and Wine's deputy in the NUP, on Thursday. Two other senior NUP figures have been reported missing for days.

Wine, 43, has said he fled his residence after a raid by security personnel shortly after the election.

Museveni is widely believed to be grooming Kainerugaba as his successor, and the military chief has previously expressed presidential ambitions.