Kampala - Ugandan police on Thursday fired teargas at students who defied a police order banning protests as they demonstrated the proposed removal of presidential age limits that would allow President Yoweri Museveni to stand again in 2021.
Police on Wednesday had issued an order banning protests in the east African county, but it was ignored by hundreds of students at the country's main Makerere University.
The students were tear-gassed, chased and detained by armed officers in return.
Ruling party lawmaker Raphael Magyezi was due to table a motion in parliament on Thursday, a first step towards passing a constitutional amendment scrapping presidential age limits - but parliament adjourned without discussing it.
Museveni, who has ruled since 1986 when he took charge at the head of a rebel army, says he is 73 years old and would be barred from running for a sixth term under the current constitution mandating candidates be between 35 and 75.
In 2005 parliament passed a constitutional amendment removing presidential term limits which allowed Museveni to stand for a third, fourth and fifth term.
Students in the capital Kampala waved branches and chanted "K'ogikwatako!" - meaning "Don't dare touch it!" in the local Luganda language - in reference to the constitutional clause on age limits.
Armed officers - including military police - fired volleys of teargas forcing the students to flee to their residence halls and hostels.
Prominent opposition politicians were also detained or arrested on Thursday, including opposition leader Kizza Besigye, who has lost four successive elections to Museveni.
Small protests also took place elsewhere in the capital and the country.
In the northern town of Lira, demonstrators left a mock coffin at a central road junction with "The removal of the presidential age limit is the death of our country" painted on the side.
On Wednesday evening Ugandan police raided the offices of a charity and a think tank which have publicly opposed the constitutional change.
US Ambassador to Uganda Deborah Malac said on Thursday she was "deeply concerned" by the situation.
"We call on the Government of Uganda to guarantee all its citizens freedom of speech, expression, and assembly, without fear of intimidation," she said in a statement.