TEGUCIGALPA, Honduras (AP) - Honduras rebuffed demands by the international community to reinstate President Manuel Zelaya and pulled out of the Organization of American States, thrusting the poor Central American nation deeper into political crisis and isolation.

Zelaya was traveling in Central America but planned to return to Honduras on Sunday, according to Nicaraguan President Daniel Ortega. Honduras' interim government has said it will arrest Zelaya if he returns, setting up a potentially volatile showdown.

About 10,000 supporters of the president ousted in a military coup June 28 again marched in his support Saturday, blocking traffic close to the presidential palace, which is occupied by a caretaker president selected by Congress to replace Zelaya, but also heavily fortified and guarded by soldiers.

Diplomats from across the Americas had hinted they would suspend Honduras' OAS membership during an emergency Saturday meeting of the organization in Washington. But after rejecting the personal appeal of the group's secretary-general, Jose Miguel Insulza, the Honduran government decided to renounce its charter rather than wait to be punished.

In a letter to Insulza read on state television Friday night, interim Honduran President Roberto Micheletti wrote that "the OAS is a political organization, not a court, and it can't judge us."

"The government rejects the attempts of the OAS to impose unilateral resolutions," said the letter read by deputy foreign minister Martha Lorena Alvarado.

Micheletti said leaving the OAS means his country will not face economic sanctions that were expected if the group's membership had been suspended. The OAS still can encourage other organizations around the hemisphere to halt aid and loans to one of Latin America's poorest countries.

Also late Friday, a grenade exploded outside Immigration offices in Tegucigalpa, the capital, smashing windows and damaging the building's facade - the fifth such explosive attack since the coup, according to police.

The letter renouncing Honduras' OAS charter capped a long and frustrating Friday for Insulza, who flew to this country to demand that the interim government restore Zelaya, who was rousted from his bed by soldiers, handcuffed and flown into forced exile. The world community has demanded his return to office.

"We wanted to ask that this situation be reversed," Insulza told a news conference after meeting with Supreme Court President Jorge Rivas, the attorney general and other political leaders. "Unfortunately, one must say that there appears to be no willingness to do this."

Insulza said Honduran officials gave him documents showing that charges are pending or have been brought against Zelaya, which they say justified the coup. The military ouster came after Zelaya pushed for a referendum on constitutional reform that the Supreme Court, the attorney general and Congress had all said was illegal.

The Supreme Court, which authorized the coup, also said it would not agree to restore the toppled leftist leader despite Insulza's personal appeals.

"Insulza asked Honduras to reinstate Zelaya, but the president of the court categorically answered that there is an arrest warrant for him," court spokesman Danilo Izaguirre said.

During the trip, the Americas' top international diplomat also met with the two main candidates in Honduras' Nov. 29 elections and with the leftist Popular Block, an umbrella group of farm, labor and student groups that largely supports Zelaya.

But he did not see Roberto Micheletti in order to avoid legitimizing the government. Micheletti has vowed to serve out the six months remaining in Zelaya's term.

Foreign Minister Enrique Ortez, said that Insulza "cannot return to Honduras, and if he does he will be arrested and tried."

Ortez also claimed that members of the Zelaya administration stole at least $40 million in cash from the Central Bank during their last day in power and announced the new government was firing at least 10 ambassadors, including those to the OAS, the United Nations, Mexico and Panama.

Micheletti's supporters say the army was justified in ousting Zelaya because he was trying to use his referendum to extend his rule. Zelaya denies that and has said he will no longer press for constitutional changes.

Nations around the world have promised to shun Micheletti and Honduras already is suffering economic reprisals.

Neighboring countries have imposed trade blockades, major lenders have cut aid, the Obama administration has halted joint military operations and all European Union ambassadors have abandoned the country.

The U.S. Embassy in Honduras issued a statement expressing "deep concern over restrictions imposed on certain fundamental rights" by Micheletti's government, including a curfew in force since the coup, and "reports of intimidation and censorship against certain individuals and media outlets."

Associated Press writers Freddy Cuevas in Tegucigalpa and Filadelfo Aleman in Managua, Nicaragua, contributed to this report.