By Jeremy McDermott
BBC News, Medellin
Colombian guerrillas have again thrust themselves onto the world stage by releasing four of the 40-odd political hostages they hold into the care of their international ally, President Hugo Chavez of Venezuela.
Hugo Chavez has played a key role securing hostage releases
"We have been practically liberated from death," said freed former congressman Orlando Beltran Cuellar.
"We are immensely thankful to President Chavez as well as to Senator Piedad Cordoba for all the motions they have made."
For a decade, the Revolutionary Armed Forces of Colombia (Farc) have collected political hostages to pressure the government into granting a prisoner exchange for guerrillas serving sentences in jails around the country.
So far, the government of President Alvaro Uribe has refused to consider the rebel demand for a demilitarised zone in the municipalities of Pradera and Florida, in the south-western department of Valle del Cauca, as a venue for talks.
The guerrilla strategy is to keep the pressure up on the government to make concessions.
"This drip-feeding of hostage releases is keeping the Farc in the international limelight," said Maria Victoria Llorente, of the Bogota-based think tank the Ideas for Peace Foundation.
"The guerrillas are trying to use the international community to force the president to give them what they want."
The other part of the rebel strategy is President Chavez.
His official role as mediator between the Farc and the Colombian government was cancelled in November last year by Mr Uribe after the controversial Venezuelan leader refused to follow the guidelines for negotiations set out by Bogota.
The Farc release of two hostages in January, and now the four politicians, has brought Mr Chavez into the centre of Colombia's 44-year civil conflict.
The Farc insist that only the Venezuelan leader can effectively act as mediator and secure real advances.
In return, Mr Chavez has described the Farc as a legitimate insurgent force and asked that the rebels be removed from international lists of terrorist organisations.
Farc rebels are holding hundreds of hostages for ransom
As shown by the rescue operations, Mr Chavez clearly has direct channels open with the guerrillas, with Colombian security forces insisting that some Farc commanders, along with those of the smaller rebel group, the National Liberation Army (ELN), are based on Venezuelan soil.
However, it is not just Venezuela that the rebels are using.
The Farc's best-known hostage, Ingrid Betancourt, is a French-Colombian citizen and former presidential candidate.
Her cause has been taken up by French President Nicolas Sarkozy, who has long been pressuring Mr Uribe to secure the release of Ms Betancourt.
"It is good for the Farc that France is pressuring for the humanitarian exchange of prisoners and keeping the issue in the political spotlight," said former Vice-Minister for Justice and newspaper columnist, Rafael Nieto Loaiza.
Kidnapping for ransom
Washington also has a crucial role to play. It is concerned about the fate of three US citizens, intelligence contractors kidnapped when their spy plane crash landed in guerrilla-dominated territory in 2003.
However, the recent convictions in the US of two Farc commanders for kidnapping will complicate the chances of securing the release of the Americans.
Gloria Polanco: Former congresswoman, 42, kidnapped in 2001
Luis Eladio Perez: Former senator, 50, kidnapped in 2001
Orlando Beltran: Former congressman, 50, kidnapped in 2001
Jorge Gechem: Former congressman, 57, kidnapped in 2002
The Colombian government is sticking to its guns, insisting it is happy to negotiate a prisoner exchange, but that there can be no demilitarised zone that the Farc are demanding as their precondition to sitting down and talking.
"We are ready to make the exchange with the conditions that we set out from the beginning," said Defence Minister Juan Manual Santos.
"There is no need for a demilitarised zone, as talks can be held anywhere in Colombia or outside of the country."
The recent releases are not likely to give any impetus to negotiations between the Farc and the Colombian government.
Mr Uribe does not want to grant a safe haven; he does not want freed guerrillas to rejoin the conflict; he does not want President Chavez to be involved in any way, while he does want to continue his "Democratic Security" policy that is dealing hard blows to the guerrillas.
Often forgotten is the plight of the estimated 700 civilians held hostage for ransom by the Farc.
Kidnapping for ransom, along with drugs and extortion, is a big earner for the guerrillas.
These hostages are not part of any exchange the Farc are proposing and they will continue to rot in the jungle until their families come up with the money necessary to secure their release.