Ugandan police on Thursday fired tear gas to disperse protesters and arrested dozens of people opposed to plans to introduce legislation that could allow the longtime president to extend his rule.
In a chaotic session in parliament, during which many lawmakers heckled and threatened each other, the house speaker said the contentious bill is likely to be introduced next week.
Uganda's constitution bars anyone over the age of 75 from seeking the presidency.
President Yoweri Museveni, 73, is ineligible to run again in 2021 if the age restriction remains. His critics accuse him of using security forces to harass the opposition, but Museveni's supporters say he enjoys wide support across the country.
The draft bill faces growing opposition from civic groups, opposition leaders and religious leaders, who have called for a national referendum before the age limit is jettisoned from the constitution.
Ugandan police had warned on Wednesday that no protests - in support of or against the president - would be allowed after it appeared that the bill would be introduced Thursday. Some opposition figures have vowed to mobilize mass support against the bill they believe is intended to enable Museveni, who has been in power for more than 30 years, to remain in office for the rest of his life.
On Thursday, amid heavy police and military deployment across the normally calm capital, Kampala, police fired tear gas at Makerere University students who were planning to stage a walk to the precincts of parliament. Among those arrested was the mayor of Kampala, Erias Lukwago, a prominent government critic.
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Ugandan police also besieged the offices of two organizations that authorities accuse of supporting anti-government protests. ActionAid and the Great Lakes Institute for Strategic Studies are suspected of "receiving funding" from unnamed sources to incite protests against the government, said police spokesman Asan Kasingye.
Police are searching the offices of the organizations for incriminating evidence, he said Thursday. It was not immediately possible to get a comment from the organizations.
In a statement Thursday, Deborah Malac, the U.S. ambassador to Uganda, urged Uganda's government to protect basic freedoms "without fear of intimidation."
"The United States is deeply concerned that recent arrests and raids stifle the Ugandan people's right to free expression and tarnish Uganda's global image," Malac said in the statement. "We are disturbed by reports of raids on NGOs."
Museveni's party has an overwhelming majority in the national assembly, so the legislation to remove the age limit is expected to pass when the procedural process starts.
Museveni, a U.S. ally on regional security over the years, took power by force 1986 following a bush war. He won re-election last year in a poll marred by allegations of vote fraud and intimidation by the security forces.
Although Museveni has warned in the past that Africa's problem was leaders "who want to overstay in power," he has since said he was speaking about leaders who were not elected.