GUANACASTE, Costa Rica - Diplomatic efforts to solve the month-long Honduras crisis stepped up Wednesday, after the United States revoked the visas of four of the country's interim officials.

The crisis was set to dominate a one-day summit of the leaders of Central America, Mexico and Colombia in Guanacaste, Costa Rica, while in Honduras, a Congress commission prepared a response to a peace plan proposed by Costa Rican President Oscar Arias.

The Organization of American States (OAS) -- which has suspended Honduras over the June 28 ouster of President Manuel Zelaya -- would meet in Washington on Friday on Honduras, a statement said.

OAS head Jose Miguel Insulza was attending the Costa Rica meeting.

The United States on Tuesday revoked diplomatic visas for four Honduras interim government officials as it sought to press them into a deal with Zelaya.

Interim Honduran officials said the list included the Supreme Court judge who signed the order to capture Zelaya and the head of Congress.

Zelaya welcomed the move from neighboring Nicaragua, where he and his supporters -- some barefoot and with no change of clothes -- have massed.

Zelaya's ouster has drawn widespread condemnation and aid freezes.

Latin American leftist leaders have however criticized the US administration for failing to take a firmer stand against the de facto regime, while some US Republican lawmakers denied that a coup had taken place.

A Honduran Congress commission Wednesday studied the Costa Rica peace proposal, although it appeared unlikely it would be approved.

Zelaya has said the Costa Rica talks have failed, while the interim leaders and the military have rejected Zelaya's return as president, a key point of the proposal.

The Supreme Court on Tuesday also rejected bringing forward elections due in November, another requirement of the accord.

Business leaders in Honduras on Wednesday slammed the financial impact of the month-long crisis, with the head of the Chamber of Commerce estimating losses of around two billion lempiras (105 million dollars).

It was unclear whether Zelaya, would make a third attempt to cross into Honduras soon.

The interim government has extended until Wednesday a curfew along the tense border with Nicaragua, while Zelaya supporters blocked a road near the border with Guatemala, according to local television.

Honduran soldiers have been ordered to arrest Zelaya if he enters the country.

The former rancher, who veered to the left after taking office, was ousted amid fears he sought to extend his rule through a referendum on the Constitution.