Men armed with assault rifles burst into a shoe factory and opened fire Tuesday, killing at least 15 workers and wounding eight, Honduran authorities said.

National police spokesman Leonel Sauceda called the attack in the northern city of San Pedro Sula "a massacre." He said the motive had not yet been determined.

Sauceda said police were not ruling out the possibility the attack may have been related to drug trafficking. San Pedro Sula has been a hotbed of gunbattles between drug traffickers and among the country's Mara street gangs.

Sauceda said at least four men using assault rifles were involved in the attack at the small shoe factory. He said 23 employees were present and all were either killed or wounded.

Also Tuesday, thousands of supporters of former President Manuel Zelaya staged street protests in the capital, Tegucigalpa, to demand the ousted leader's return as well as a 15 percent rise in the minimum wage, currently about $290 a month.

Zelaya was removed in a June 2009 coup, and his term expired in January. He was replaced by Porfirio Lobo, who won a fall presidential elections that had been scheduled before Zelaya's ouster.

Lobo has said Zelaya, who has been living in the Dominican Republic, is welcome to return to Honduras, but says he must face charges of fraud, usurping other institutions' powers and falsifying documents.

The demonstrators included unionized workers, government employees and students. They blocked traffic in at least two points in the city, and demonstrations were held in other cities.

One small group of masked protesters shattered windows at a television station, the offices of the country's Human Rights Commission and a bank branch.