Southern separatists in Yemen set fire to a tent camp housing anti-government protesters in the port city of Aden, witnesses said on Sunday, in opposition to an election this month to replace outgoing President Ali Abdullah Saleh.
Southern separatists joined protesters calling for Saleh to leave last year, but the two sides have since grown apart.
The separatists want to revive a southern socialist state that was united with the north in 1990. They fear the February 21 election will not serve their goal.
Anti-Saleh demonstrators broadly back the vote as a step towards ending his 33-year rule.
Witnesses said hundreds of separatists marched through Aden, in southern Yemen, late on Saturday, setting fire to tents in the camp of about 100 protesters. About 10 people were injured.
Weakened by months of protests, the Yemeni government has lost control of whole chunks of the country.
Saudi Arabia and the United States are keen for the election to go ahead, fearing protracted instability in Yemen is giving al Qaeda's Yemen-based wing room to expand their foothold there, near oil shipping routes through the Red Sea.
But Northern Shi'ite rebels have said they too will boycott the vote, in which acting leader Abd-Rabbu Mansour Hadi is the sole candidate to fill Saleh's position.
Saleh is in the United States receiving medical treatment for injuries inflicted during an assassination attempt on him, but has said he will return home before the vote, shedding doubt on his commitment to leave office in line with a Gulf-brokered plan to end a year of political upheaval.
The Southern separatists accuse northerners of monopolising power and usurping their resources.
Three separatist groups issued a statement denouncing the tent camp attack as a northern ploy to weaken the southern campaign for independence.
We ask all sides not to be dragged into a colonialist plot aimed at turning the struggle of our people against the (northern) coloniser into a south-south struggle, they said in a statement.
Saleh's forces crushed a southern attempt to break away in 1994.
Islamist militants executed early on Sunday three men they accused of giving the United States information used to carry out drone strikes in the area, a spokesman for the group said in a text message.
(Reporting by Mohammed Mukhashaf; Writing by Isabel Coles; Editing by Alessandra Rizzo/Ruth Pitchford)