Kampala - Ugandan police on Thursday fired tear gas to disperse protesters opposed to plans to introduce legislation that could allow the longtime president to rule for life.The bill is likely to be introduced in the national assembly later on Thursday despite growing opposition from religious leaders, civic groups and opposition leaders.Ugandan police had warned on Wednesday that no protests — in support of or against the president — would be allowed. But some opposition figures have vowed to mobilise mass support against a bill they believe is intended to enable President Yoweri Museveni to remain in power for the rest of his life despite having already ruled the East African country for more than three decades.Uganda's constitution bars anyone over the age of 75 from seeking the presidency. Museveni is 73 and ineligible to run again in 2021 if the age hurdle remains.His critics accuse him of using the security forces to harass the opposition, but Museveni's supporters say he enjoys wide support across the country.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.Funding Ugandan police also besieged the offices of two NGOs that the 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 NGOs for incriminating evidence, he said on Thursday.It was not immediately possible to get a comment from the NGOs.Museveni's party has an overwhelming majority in the national assembly — the reason legislation to remove the age limit is expected to pass when the procedural process starts.Museveni, a US 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 are not elected.