By Jeremy McDermott BBC correspondent in Bogota

The guerrillas of the Revolutionary Armed Forces of Colombia (FARC) failed to assassinate Alvaro Uribe as he campaigned for the presidency.

If they [the FARC] cannot wreck Wednesday's inauguration, they have vowed to make the Uribe administration the most bloody to date

But they have not given up their efforts to murder him as he prepares to takes up office on Wednesday.

The upcoming inauguration needs no publicity, as the FARC are heralding its approach by stepping up their campaign of urban terror, and have detonated seven bombs in the country's major cities.

The Colombian secret police, the DAS, claimed to have uncovered a plot to wreck the inauguration, after arresting six members of the FARC's urban militia.

"The persons, according to intelligence reports, are from the FARC's special forces, who were seeking to realise terrorist attacks in the capital with the aim of derailing the presidential inauguration of Alvaro Uribe," said Javier Ramos, the DAS head of public security.

The six were captured with guns with telescopic sights, grenades and ammunition.

'11 September re-run'

The secret police insist there is a plan to use mortars against the presidential palace, either as Mr Uribe lands in a helicopter or during the inauguration ceremony.

"We know of a direct order from the secretariat [ruling body] of the FARC to attack the presidential helicopter," said Mr Ramos.

The security forces are taking the threats seriously, as is the United States, which will be enhancing security by providing surveillance aircraft to fly over the capital on Wednesday.

"In response to a Government of Colombia request, the US Government is providing a P3 aircraft from the US Customs Service during the inauguration, to help alert Colombian officials to any violation of the no-fly zone surrounding Bogot�," the US Embassy said.

It was commenting after the DAS last week accused the FARC of planning to fly a plane packed with explosives into the presidential palace, in imitation of the 11 September attacks in the US.

Uribe's nine lives

In the three major cities in Colombia, the capital Bogota, Medellin and Cali, the security forces have announced plans to seal the urban centres in what is known in Cali as "Operation Padlock".

Mr Uribe has been a FARC target since he was governor of the war-torn province of Antioquia in the mid 1990s.

During his governorship, the FARC were driven from the rich banana-growing area of Uraba by right-wing paramilitaries allegedly working with the security forces.

In April this year, the FARC set off a car bomb along the route Mr Uribe was travelling whilst on campaign in the Caribbean city of Barranquilla.

Mr Uribe was saved by the armour on his bullet-proof jeep, but five passers-by were killed and 13 wounded in the attempt.

Daggers drawn

Mr Uribe won the presidency with a promise to get tough on the FARC and has secured backing from the US by presenting himself as the newest and keenest recruit in the war on terrorism. Three of Colombia's warring factions are on the US terrorism list.

The US has increased military aid to Colombia, voting in an emergency supplement of $440 million, and lifted restrictions on a billion pounds worth of military aid granted by President Clinton, which was for use only in the war on drugs.

Mr Uribe is for them [the FARC] the most hated president yet

Added to this, the US is planning another $500 million for Colombia in the next fiscal year.

But all of this has not daunted the FARC - on the contrary, it seems set to provoke them to even greater heights of violence, particularly urban violence.

Colombian military sources insist the FARC have been trained in urban operations by the Irish Republican Army (IRA), and that an urban offensive is planned by the rebels using the new tactics.

Three alleged members of the Irish group are languishing in prison in Bogota at the moment awaiting trial for training the FARC in explosive and urban terrorism.

The FARC have marked the entry into office of the last two presidents with frenzied attacks and Mr Uribe is for them the most hated president yet.

If they possibly can, the rebels will seek to show that they cannot be intimidated by his tough talk and US backing.

And even if they cannot wreck Wednesday's inauguration, they have vowed to make the Uribe administration the most bloody to date.