KAMPALA, Uganda (AP) — Human Rights Watch and other rights groups are urging Ugandan authorities to free a prominent rights attorney who is being held by police over criminal allegations.

Nicholas Opiyo, who has represented opposition figures and minority groups, was arrested on Tuesday while eating at a restaurant in a suburb of Kampala, the capital. Police say he is held on charges of “money laundering and related malicious acts.” Opiyo is yet to be officially charged.

Critics of long-serving President Yoweri Museveni see the arrest as part of a campaign of repression targeting perceived government opponents ahead of presidential elections in January. Opiyo has previously represented Bobi Wine, the singer and lawmaker who is Museveni’s main challenger.

Local media report that Opiyo has been representing at least two civic groups whose bank accounts were recently frozen by authorities who accused the groups of alleged terrorist activities.

The arrest “sends a chilling message about (authorities') disregard for basic rights," Human Rights Watch said in a statement.

Chapter Four Uganda, a group led by Opiyo, said it was “deeply concerned about the abduction and incommunicado detention."

Clement Voule, the United Nations special rapporteur on freedom of association and peaceful assembly, said on Twitter that he was very concerned by "the increasing crackdown” on civic groups as well as those who represent dissenting voices in Uganda.

Museveni has ruled Uganda for 34 years. Although he remains popular in some rural parts of the country, he has struggled to win over impoverished, jobless Ugandans in urban centers who have rallied behind opposition figures such as Wine, whose real name is Kyagulanyi Ssentamu.

Museveni is able to seek more time in office after lawmakers removed the last constitutional obstacle — age limits — to a possible life presidency for the 76-year-old leader.