SANAA, Yemen - Witnesses say police opened fire Thursday to break up an anti-government protest, and security officials said one protester was critically wounded.
It was not immediately clear whether the police were using live ammunition or rubber bullets.
Two other demonstrators were wounded in the eastern town of Mukalla, but no details were immediately available, officials said.
The protest in Mukalla was one of several anti-government demonstrations across Yemen. Tens of thousands joined in the protests, chanting "Down, down with the regime."
Thursday's marches were among the largest yet against President Ali Abdullah Saleh, a key U.S. ally in the fight against al-Qaida. Earlier this week, the president, in an attempt to defuse calls for his ouster, promised not to extend his term beyond 2013.
Opponents and supporters of Saleh staged dueling demonstrations, underscoring deep divisions in the nation.
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 the capital, Sanaa, and other cities yesterday to demand the ouster of Saleh, a longtime autocrat.
"Thirty years of promises and thirty years of lies," one protest banner read.
Estimates of the number of anti-government protesters ranged in the several tens of thousands. 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.
Some in the pro-government group were state employees.
Saleh pledged Wednesday not to seek another term in office - his term expires in 2013 - and said he would not let his son inherit power. However, proposed amendments to the constitution could let Saleh 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.
The United States cautiously praised reform pledges in Yemen. Saleh is seen as a weak but increasingly important partner of the United States, allowing American drone strikes on al-Qaida targets and stepping up counterterrorism cooperation.