Yemen - Yemeni troops killed two people on Thursday when they opened fire on a rally in the southern province of Dalea calling for a boycott of an election to replace outgoing President Ali Abdullah Saleh, activists said.

Weakened by months of protests against Saleh's rule, the Yemeni government has lost control of whole chunks of the country, giving southern separatists, northern Shi'ite rebels and Islamist militants a window to further their goals.

A senior officer was killed late on Thursday in a hail of bullets fired by militants riding motorcycles, said witnesses in the southern province of Lahej, underscoring the security challenges Yemen faces as it prepares to go to the polls.

Separatists seeking to revive a southern socialist state that Saleh united with the north in 1990 have been demonstrating against the vote, scheduled for February 21, and northern Shi'ite rebels have also said they will not take part.

"The army forces located at military positions overlooking the town opened fire on thousands of people protesting against the upcoming presidential elections," a leader of the southern separatist movement told Reuters.

"One demonstrator died immediately and another 12 were injured, while another man who was standing on the balcony of a hotel adjacent to the electoral committee's office was killed by a stray bullet."

The election is part of a plan hammered out by Yemen's Gulf neighbors to end a year of political upheaval.