Q&A: Colombia's civil conflict
Colombia has suffered decades of civil conflict and has long been a major producer and exporter of illegal drugs such as cocaine.
Former President Alvaro Uribe, in office from 2006 to 2010, pursued a hard-line stance against left-wing guerrillas while making tentative peace overtures.
His successor, Juan Manuel Santos, took office in 2010 vowing to seek an end to the conflict. In October 2012, the government and the biggest rebel group, the Revolutionary Armed Forces of Colombia (Farc), launched peace talks.
Why has Colombia long suffered high levels of violence?
Colombia, in common with many Latin American nations, evolved as a highly segregated society, split between the traditionally rich families of Spanish descent and the vast majority of poor Colombians, many of whom are of mixed race.
This group provided a natural constituency for left-wing insurgents - with two main groups, the Farc and the ELN (National Liberation Army).
At the other end of the political spectrum were right-wing paramilitaries, with roots in vigilante groups set up decades ago by landowners for protection against rebels. The main group was the AUC - the United Self-Defence Forces of Colombia, which officially at least has demobilised.
In a country where the presence of the state has always been weak, the result was a grinding war on multiple fronts, with the civilian population caught in the crossfire and often deliberately targeted for "collaborating".
Human rights advocates blamed paramilitaries for massacres, "disappearances", and cases of torture and forced displacement. Rebel groups are behind assassinations, kidnapping and extortion.
What is the situation today?
The Farc, the country's largest rebel group, and the government are holding peace talks in the Cuban capital, Havana. After six months of talks, they reached agreement on land reform, one of six major issues on their agenda. Negotiations continue, but President Juan Manuel Santos has set a deadline of November 2013 for significant agreement to be reached.
The rebels, although much weakened, are still active. The Farc had called a unilateral two-month ceasefire when talks began in November as a sign of good will. But with the government refusing to cease military operations, the rebels restarted their attacks on military and civilian targets in January. The government insists that there will only be a ceasefire when a peace agreement is signed.
Another factor has been the emergence of what the government calls Bacrims, namely criminal bands, which are involved in drug-trafficking and extortion. These groups emerged after the demobilisation of the AUC paramilitaries in 2006.
The cocaine trade has been the main motor of the armed conflict, providing hundreds of millions of dollars in funding for the illegal armed groups.
It is difficult to find reliable statistics on the toll from the violence in Colombia. What is clear is that the scale of the suffering has been huge.
Especially at risk are those with high-profile roles in the community - including social leaders, political activists, human rights campaigners and trade unionists. Many indigenous communities have also suffered attacks.
Violent crime and kidnappings have, however, decreased in recent years. In May 2008, the government announced that kidnaps were at a 20-year low. Figures showed that from a high in 2000, when more than 3,500 people were seized, in 2007 just under 400 people were kidnapped. Of these, some 179 were freed.
But the fate of those taken hostage by rebels or seized by common criminals continues to resonate in Colombian society.
Over the decades, some three million people have been internally displaced by the fighting.
The UN says that many displaced people often end up living in shanty towns around the cities, where they have little access to health or educational services.
What are the prospects for peace?
There have been many attempts at negotiations over the course of the conflict, but to date these have always faltered.
The tough security policy pursued by former president Uribe and Mr Santos, then his defence minister, inflicted significant blows on the rebels. Several rebel leaders died and there has been a high number of desertions from guerrilla ranks.
However, the rebels do still operate across large rural areas, where the presence of the state is weak.
The latest round of peace talks has been described as more realistic than previous attempts. The talks between the Farc and government representatives centre on five key issues: rural development; guarantees for the exercise of political opposition and citizen participation; the end of armed conflict; drug trafficking; and the rights of the victims of the conflict.
So far, they have reached agreement on the first of the six issues: land reform. However, with negotiations taking more than half a year to reach a deal on one point, it is difficult to see how the two parties can stick to their original schedule unless they considerably speed up the pace.
Even if the government signs a peace deal with the Farc, it will still have to deal with Colombia's second largest rebel group, the National Liberation Army (ELN).
The ELN, has expressed interest in entering peace negotiations but President Santos said he wanted to see "actions rather than words" and demanded the 3,000-strong rebel force release the hostages it still holds, including a Canadian citizen.
What about paramilitary fighters?
Since 2003, some 31,000 paramilitaries handed in their weapons under a peace deal.
A controversial justice and peace law passed in 2005 meant that paramilitary fighters were eligible for reduced jail terms - of no more than eight years - if they gave details of their involvement in torture, killings and other crimes.
Critics argued that paramilitaries guilty of serious human rights violations could end up serving only token jail terms.
The government points to figures which it says show a decreasing level of violence as evidence that its strategy is working.
The extent of the paramilitaries' influence over and involvement in local, regional and national politics came to the fore in 2007. In a scandal dubbed the "parapolitics", a dozen members of congress were jailed and dozens more politicians investigated for links to the AUC.
Why is the US involved in Colombia?
More than 90% of all cocaine on American streets comes from Colombia, so the US administration is keen to tackle the supply at source.
Since 2000, Washington has spent several billion dollars on training and equipping Colombian forces, and providing intelligence to help tackle drug traffickers and eliminate coca crops.
Human rights groups say the line between the war on drugs and the war on rebels has been increasingly blurred.
They say Colombia's rebels have been disproportionately targeted in Plan Colombia, though it is the paramilitaries who have been most involved in drug-trafficking.
The US and Colombia signed a controversial deal in October 2009 to allow the US military use of several Colombian airbases.
The two countries said this was to counter drug-trafficking and terrorism. But some of Colombia's neighbours expressed concern at what they saw as an increased US military presence in South America.