TEGUCIGALPA - Honduran security forces clashed on Tuesday with thousands of supporters of ousted President Manuel Zelaya outside Brazil's embassy, where he took refuge after slipping back into the country aiming to retake power.

Several hundred troops and police, some firing tear gas, cleared away rock-throwing demonstrators from the embassy. Twenty people were injured before security forces took control of the area and settled in for what might be a long standoff.

Leftist Zelaya sneaked back into Honduras on Monday, ending almost three months of exile after he was toppled in a coup and bringing the world's attention to his cause again.

The embassy is surrounded by police and the military ... I foresee bigger acts of aggression and violence, that they could be capable of even invading the Brazilian Embassy, Zelaya said in an interview with Venezuelan broadcaster Telesur.

Honduras' pro-coup government wants to arrest Zelaya, a close ally of Venezuelan President Hugo Chavez, and charge him with corruption and trying to change the constitution.

Security forces blasted the embassy for 15 minutes with a high-pitched sound from a speaker perched in a truck but Honduras' de facto leader, Roberto Micheletti, said he would stop short of ordering the storming of the embassy.

We will do absolutely nothing to confront another brotherly nation, Micheletti told Reuters [nN2248544]. We want them to understand that they should give him political asylum or turn him over to Honduran authorities to be tried.

The United States, the European Union and the Organization of American States have called for dialogue to return the Central American country to democratic rule.

But Micheletti, a bitter rival of Zelaya who was named president by Congress on the day of the coup, said the leftist had first to hand himself over to legal authorities before any talks. He said Zelaya could stay holed up in the embassy for five to 10 years.

The de facto leader rejected international calls for a negotiated settlement that would allow Zelaya to return with limited powers ahead of the scheduled presidential election in November.

Zelaya will never return to be president of this country, he said.

U.S. URGES CALM

The streets of Tegucigalpa were mostly empty with public transportation, schools and shops closed down after the standoff.

The United States, an ally of Honduras during the Cold War, urged calm.

The United States calls on all parties to remain calm and avoid actions that might provoke violence in Honduras and place individuals at risk or harm, said State Department spokesman Ian Kelly.

Latin American leftist governments have accused President Barack Obama of not doing enough to force Zelaya's return to power.
Obama has cut U.S. aid to Honduras since the coup and pushed for Zelaya's return but refused his demands for tougher sanctions against the coup leaders.

Brazilian President Luiz Inacio Lula da Silva said Brazil would protect Zelaya's right to seek refuge.

Brazil is guaranteeing that he stays there -- that is an international right and we do not expect the coup leaders to touch the Brazilian embassy. We expect them to negotiate, said Lula, in New York to attend the U.N. General Assembly.

Foreign Minister Celso Amorim said Brazil might ask the U.N. Security Council to discuss the safety of the diplomatic mission in Honduras.

(Additional reporting by Deborah Charles in Washington, Walter Brandimarte in New York and Mica Rosenberg in Mexico City; Writing by Alistair Bell; Editing by Bill Trott)