SANAA, Yemen – Yemeni police armed with sticks and daggers on Sunday beat back thousands of protesters marching through the capital in a third straight day of demonstrations calling for political reforms and the resignation of the country’s U.S.-allied president.

The protests have mushroomed since crowds gathered Friday to celebrate the ouster of Egyptian President Hosni Mubarak after a revolt fueled by similar grievances.

Police used truncheons to stop protesters, many of them university students, from reaching the capital’s central Hada Square. Witnesses said plainclothes policemen wielding daggers and sticks also joined security forces in driving the protesters back.

The Ministry of Interior called on people not to heed “suspicious calls for chaos” and to avoid rallies which “obstruct the course of daily life.”

Yemen’s president, Ali Abdullah Saleh, also postponed a trip to Washington scheduled for next month due to the “circumstances in the country,” the state news agency reported.

Much is at stake in Yemen – a deeply troubled nation strategically located at the mouth of the Red Sea and next door to the world’s largest oil reserves. Saleh’s weak government is already under pressure from a southern separatist movement and disaffected tribesmen around the country.

Opposition parties set several conditions for joining talks with the government, including a definitive timetable for “constitutional, legal and economic reforms.”

The parties also demanded that Saleh remove his sons and other relatives from army, security and government posts.

Saleh has tried to defuse the unrest by promising not to run again when his term ends in 2013 and guaranteeing that he will not seek to pass power on to his son.