As tens of thousands marched in Sana'a, scuffles and stone-throwing erupted briefly between backers of President, Ali Abdullah Saleh and his opponents.
Yemen government supporters and opponents hold rival rallies
SANAA // Tens of thousands of opponents and supporters of Yemen's president staged rival demonstrations today in the country's capial.
Scuffles and stone-throwing erupted briefly between the two sides, but police intervened to keep the sides apart and there were no reported casualties.
Egypt's turmoil and the revolt in Tunisia inspired Yemen's opposition, who turned out in unprecedented numbers in Sanaa and other cities to demand the departure of the longtime president, Ali Abdullah Saleh.
"Thirty years of promises and thirty years of lies," one protest banner read. Protesters chanted: "Down, down with the regime."
Estimates of the number of anti-government protesters ranged in the several tens of thousands. However, pro-government demonstrations, though smaller, reflected a calculated effort to undercut the opposition, possibly a lesson learned from the huge street rallies that have rocked the Egyptian government since January 25.
Some in the pro-government group were state employees.
Mr Saleh had sought to defuse demands for his ouster by pledging on Wednesday not to seek another term in office - his term expires in 2013 - and saying he would not let his son inherit power. However, proposed amendments to the constitution could let SMr aleh stay in office for two additional terms of 10 years.
Anti-government protesters, several thousand of whom marched from Sanaa University, said they don't trust Saleh and demanded that he quit immediately.
Mr Saleh is seen as a weak but increasingly important partner of the US, allowing American drone strikes on al Qa'eda targets and stepping up counterterrorism cooperation.
His weak government, which controls little of the impoverished country beyond the capital, is also facing a serious challenge from a secessionist movement in the south and a rebellion in the north.
The US-born radical cleric Anwar al Awlaki, thought to be hiding in Yemen, is believed to have inspired and even plotted or helped coordinate recent attacks on the US Those include the failed Christmas Day 2009 bombing of a Detroit-bound airliner and the unsuccessful plot to send mail bombs on planes from Yemen to the US in October.
Al Awlaki also is believed to have inspired the deadly 2009 shooting rampage at Fort Hood, Texas, and had ties to some of the 9/11 hijackers.
In San'aa, pro-government demonstrators marched to Tahrir Square, which shares the same name as the plaza in Cairo where the street fighting occurred Wednesday and into Thursday. The demonstrators carried banners supporting Saleh and warning that the opposition was trying to destabilize Yemen.
There was a heavy security presence around the interior ministry and the central bank. Military helicopters hovering in some areas.
In the city of Aden, thousands of anti-government protesters defied security forces and armoured personnel carriers that tried to close the main streets to prevent them from gathering.
Protesters there shouted: "People want the downfall of the regime, the downfall of the president."
All big shops in Sana'a and Aden closed their doors and major companies hired guards to protect against possible looting.
Protesters also scuffled with security forces in the town of Jaar in the southern province of Abyan, where al Qa'eda militants have been active.