Yemen's president has said he has ordered his security services to protect protesters, stop all clashes and prevent direct confrontation between government supporters and opponents.
The directive came after security forces in the southern port of Aden used tear gas and fired bullets in the air to disperse hundreds of protesters, and government supporters wielding clubs attacked demonstrators in the capital Sanaa.
Amnesty International said two people were killed in Sanaa, the first fatalities in the capital since unrest began about two weeks ago.
Yemen, an impoverished country with an active branch of al Qaida, has been swept up in the protests inspired by successful uprisings in Egypt and Tunisia.
The demonstrators are demanding that US-backed President Ali Abdullah Saleh, in power for 32 years, step down, but he has said he will stand down after national elections in 2013.
"The Government of the Republic of Yemen will continue to protect the rights of its citizens to assemble peacefully and their right to freedom of expression," Mr Saleh said in a statement issued by Yemen's embassy in Washington.
On Wednesday, thousands streamed into a square in Sanaa to bolster anti-government protesters after club-wielding backers of Mr Saleh tried to drive them out.
In the Red Sea port of Hodeida, Saleh supporters attacked a group of anti-government protesters injuring at least 10, according to activists who were taking part in the demonstration.
Security forces in the southern port of Aden used tear gas and fired bullets in the air to disperse hundreds of protesters, officials said.
Seven people who belong to Mr Saleh's ruling Congress Party resigned from the group because of the situation in the country and said they will form their own independent bloc, member of parliament Abdul-Aziz Jabbari said.