By Jeremy McDermott
BBC News, Medellin
The rebels have carried out several recent bomb attacks
After suffering a series of bitter defeats in 2008, rebels of the Revolutionary Armed Forces of Colombia (Farc) have launched what they call "Plan Rebirth", Colombian officials say.
The rebels have brought their 45-year conflict back into the cities, with four bomb attacks so far this year.
They have also stepped up their extortion demands and their hold on the drugs trade, according to the government.
But do these actions signal that the rebels are regrouping, or rather that they are a spent force?
2008 was the most damaging year for the Marxist Farc in four decades of fighting, giving rise to hopes that the brutal civil conflict might really be coming to an end.
In 2008 the head of the armed forces, General Freddy Padilla, said that "the end of the Farc is in sight".
Defence Minister Juan Manuel Santos has echoed this sentiment, insisting that the rebels are in their death throes.
Farc's founder, Manuel Marulanda, died in 2008 from a heart attack
"This plan seeks to give the sensation, through terrorist acts, that the Farc are still alive and kicking," said Mr Santos, a presidential hopeful for the 2010 elections.
"They want to show that they are stronger than they really are. But this 'Plan Rebirth' and terrorism just shows their weakness."
Last year two members of the Farc's seven-man ruling body, the Secretariat, were killed.
One - Raul Reyes - died during an aerial bombardment of his camp, just across the border in Ecuador. The incident led to a severing of diplomatic relations between Colombia and Ecuador, which have still not been renewed.
The other, the youngest member of the Secretariat, Ivan Rios, was killed by his own bodyguard who then cut off the dead man's hand to prove to authorities what he had done and collect a reward of some $300,000 (£210,000).
The Farc's legendary founder and leader Manuel Marulanda, alias "Sureshot", also died in 2008, of a heart attack.
He founded the guerrilla group in 1964, building it up from a few dozen relatives and friends to an army of 16,000 fighters which controlled up to a third of the country at its height in 2002.
Other blows to the Farc in 2008 were offensives by the US-backed Colombian army and then the daring rescue, last July, of 15 hostages including French-Colombian citizen Ingrid Betancourt.
The freeing of Ingrid Betancourt was a major blow to the Farc in 2008
All these events, plus a breakdown in communications between Farc units, led to an unprecedented wave of desertions with more than 3,000 rebels surrendering to take advantage of generous government amnesty guarantees, according to government figures.
However, not everyone is convinced that the Farc is facing defeat.
This year the rebels have begun to make their presence felt again by increasing their extortion demands.
Those that do not pay are attacked. Even large companies like French supermarket giant Carrefour and DVD-rental chain Blockbuster, which saw one of its outlets destroyed in a blast that killed two.
Targets were not in the remoter parts of the country where the Farc have influence, but in Bogota, indicating that the rebels have the ability to reach into the heart of the capital.
The Farc also has a new leader: Alfonso Cano.
Big and bearded, Mr Cano has more of a reputation as a political ideologue than a warrior, but is known as a strategist and long-term thinker.
Last year he needed to assert his authority within the movement, develop a new tactical plan and get the orders out to his units.
"In 2009 we must force ourselves to retake the initiative, in the political as well as military fields," Mr Cano said in a communique published in January.
Last October, security forces captured several laptop computers and memory sticks that outline the new rebel strategy and the focus of Plan Rebirth, including:
- increase urban attacks
- wage a war of attrition on two fronts. The first is military, using homemade anti-personnel mines and snipers to increase army casualties and undermine morale and secondly economically by attacking infrastructure just as the global credit crisis begins to be felt in the country
- build up finances through extortion and drug-trafficking
- expend more effort on political indoctrination to counter growing desertion
- consolidate territorial control, particularly in the areas where drugs crops are grown
- launch a campaign of political work, both nationally and internationally, to recover lost ground and increase followers, particularly in urban areas
The Farc is certainly a leaner army now, down to perhaps 8,000 fighters from more than double that in 2002.
Finances have been hit along with morale. However, a leaner Farc may well turn out to be harder to hit.
Rebels have been planting roadside bombs that target patrols by soldiers and police officers, and laying homemade anti-personnel mines that are almost impossible to detect.
The Farc is not going to disappear any time soon.
President Alvaro Uribe, who has vowed to crush the rebels, recently said that he would not sit down to talk to the Farc until they released all the hostages they held - 22 servicemen and hundreds of others being held for ransom.
That is not going to happen soon, and so neither is an end to this conflict.