TEGUCIGALPA - A Honduran teacher died three days after he was shot in the head while protesting the ouster of President Manuel Zelaya, as the military-backed regime threatened to crackdown on future demonstrations.

Roger Abraham Vallejo, 38, who was shot Wednesday during a protest in the Mercado Zonal Belen, in northern Tegucigalpa, succumbed to his injury on Saturday.

Witnesses have said he was shot when hundreds of police officers charged a crowd of pro-Zelaya marchers.

"All I know is that the police killed him for struggling for a just cause," his 78-year-old mother Maria Soriano told AFP, as hundreds of Zelaya sympathizers crammed into a hall to mourn Vallejo.

Vallejo became the third Zelaya supporter killed since the leftist president was bundled out of his bed at gunpoint and kicked out of the country in a military-supported June 28 coup.

"The blood that is being spilled will not be in vain, because we are going to fight tirelessly" to reverse the military-supported coup, said Zelaya, from the Nicaraguan town of Ocotal, on the border with Honduras.

"The people have the right to insurrection when someone takes power by force of arms, and we are using that right," Zelaya said.

The ousted president is organizing what he has called his "Popular Peaceful Army," made up of hundreds of Hondurans who crossed into Nicaragua to support his cause.

He threatened the interim Honduran regime with "generalized violence" on Friday if the coup was not reversed.

Honduran police, perhaps anticipating further clashes, warned late Saturday that they would fully enforce the Honduran penal code forbidding protest marches "when they could affect free circulation and the rights of others."

People who organize or lead "in an illicit manner any demonstration" face up to four years prison and hefty fines, the statement read.

The coup has been roundly condemned abroad, and the regime, headed by acting president Roberto Micheletti, is finding itself increasingly isolated.

Costa Rican President Oscar Arias -- who won the 1987 Nobel Peace prize for helping broker peace in Central America -- has failed up to now in his attempt to negotiate a deal between Zelaya and Micheletti to solve the crisis.

On Sunday Spain's First Vice President Maria Teresa Fernandez de la Vega is scheduled to arrive in Costa Rica, with the Honduras crisis on the agenda.

Enrique Iglesias, the long-time former head of the Inter-American Development Bank (IDB) and current senior official with the Ibero-American Cooperation Secretariat, is also set to arrive Sunday to discuss Honduras, an official in San Jose told AFP.

Micheletti meanwhile said he was surprised that Zelaya had taken to the hills and "called for an insurrection."

And in an interview with local HRN news he criticised the United States' line, saying he was surprised at US support for Zelaya.

Washington has said that Zelaya is the country's only president. US ambassador to Honduras Hugo Llorens even flew to Nicaragua and traveled to the border to meet the deposed president last week.

"We are extremely surprised with the attitude taken by the (US) ambassador, and we call on him for a correction; he cannot be interfering in issues that are strictly of Honduras," Micheletti said.

"There is no country or people powerful enough in the world to bend us," he added.

Washington has canceled diplomatic visas for four members of the interim government, and Micheletti on Friday threatened to retaliate by canceling the visas of US diplomats.

Meanwhile representatives of several foreign human rights groups visiting Honduras called on authorities to "respect" the demonstrators.

Group members included activists from Spain, Argentina, Brazil, France and El Salvador.