KAMPALA - The Ugandan military on Thursday sentenced seven soldiers to up 90 days in jail after they were convicted of assaulting journalists who were covering an event outside a U.N. office in the capital Kampala.

Punishment of security personnel for abuse against journalists is rare and attacks on reporters have escalated in recent months amid a crackdown on supporters of opposition leader Bobi Wine.

On Wednesday, soldiers descended on a group of journalists outside the U.N. High Commissioner of Human Rights office, beating and injuring at least 20 of them.

NTV Uganda television showed the journalists running for safety and screaming as the security personnel struck them with batons. Four of those assaulted sustained serious injuries including to the head.

The journalists were covering Wine, a pop star and lawmaker, as he delivered a petition to the office asking the United Nations to investigate human rights violations on the country including torture, abductions, illegal detentions and others.

The Uganda Peoples' Defence Forces (UPDF) said in a statement that a military disciplinary committee had tried the seven soldiers, who included a captain, convicted and given them varying sentences ranging from a severe reprimand to 90 days in jail.

Military chief, General David Muhoozi, had apologised for the incident and vowed to punish the culprits.

"Such actions are regrettable and the UPDF as a professional institution doesn't condone such acts," Muhoozi said in a statement.

Wine, whose real name is Robert Kyagulanyi, has earned the wrath of President Yoweri Museveni after galvanising a large following among the country's youth and emerging as formidable political opponent.

He lost to Museveni in last month's election and rejected the result, saying there was widespread rigging that included pre-ticking of ballots, falsifying results on tally sheets, intimidating his agents and other irregularities.

He has challenged the results in court.