Honduran forces tightened the border with Nicaragua against an attempt by deposed President Manuel Zelaya to enter the country after he was removed in a coup.

Honduras' military expelled Zelaya from the country in a June 28 coup after the Congress and Supreme Court accused him of violating the constitution by trying to lift limits on presidential terms. Congress appointed its leader, Roberto Micheletti, to replace Zelaya.

Costa Rican President Oscar Arias is mediating between the sides in Central America's worst crisis since the Cold War.

Here is a timeline of events in the crisis:

June 24 - President Manuel Zelaya fires military chief of staff Gen. Romeo Vasquez after the army refused to help distribute ballots for an unofficial referendum on overhauling constitution in part to allow for presidential re-election. The Supreme Court had already ruled the vote illegal.

June 25 - The Supreme Court rejects Zelaya's firing of the head of the army and orders Vasquez reinstated. Zelaya leads a group of rowdy supporters to storm a military base to take the ballots by force and vows to move ahead with the vote.

June 28 - On the day of the referendum vote, soldiers arrest Zelaya in an early morning raid on his house and expel him in his pyjamas on a flight to Costa Rica.

-- Honduran Congress names Micheletti interim president. Supreme Court says it ordered the army to remove Zelaya.

-- The European Union condemns the coup d'etat.

-- Venezuelan President Hugo Chavez, a Zelaya ally, puts his troops on alert and vows to respond militarily if his ambassador to Honduras is kidnapped or killed.

June 29 - U.S. President Barack Obama says the coup is illegal and will set a terrible precedent of transition by military force unless it is reversed.

-- At a meeting in the Nicaraguan capital Managua, leftist Latin American countries say they will withdraw their ambassadors from Honduras.

June 30 - The United Nations General Assembly calls on member states to recognize only the Zelaya government. Zelaya says he has vowed to return to Honduras.

July 4 - The Organization of American States meets in Washington and suspends Honduras after the interim authorities ignore an ultimatum to reinstate Zelaya.

July 5 - At least one pro-Zelaya protester is killed and two wounded in clashes at Tegucigalpa's airport as Honduran troops block an attempt by Zelaya to return home in a plane provided by Chavez. Zelaya lands in Managua instead.

July 6 - The United States condemns violence against protesters in Honduras and calls for Zelaya's reinstatement.

July 7 - Micheletti and Zelaya accept Costa Rican President Oscar Arias as a mediator to try to resolve the crisis.
July 8 - The U.S. government suspends $16.5 million in military assistance programs to Honduras. It said an additional $180 million in aid could also be at risk.

July 9 - Micheletti and Zelaya travel to Costa Rica to discuss the crisis with Arias but never meet face-to-face. Delegations from rival sides remain to continue talk.

July 19 - Talks are reconvened in Costa Rica with neither leader attending but break down after two days of talks.

-- Arias requests more time to come to a resolution and says he will not give up hope for a negotiated settlement.

-- Zelaya pledges to return to Honduras on the weekend of July 25-26.

July 22 - Rival governments open new talks and in a sign of flexibility, the pro-coup delegation says it will let the Honduran Congress and judiciary consider a proposal to let Zelaya return. However foreign minister Carlos Lopez, again swore Zelaya will not be allowed to return.

July 23 - Zelaya leaves the Nicaraguan capital Managua along with a convoy of supporters and journalists and heads north for the Honduran border.

July 24 - Honduran soldiers tighten border with Nicaragua against an attempt by Zelaya to enter the country.

(Writing by David Cutler, London Editorial Reference Unit and Mica Rosenberg in Mexico City;)