President Clinton promised that the US "is not going to get into a shooting war" as he brought a $1.3 billion aid package for Colombia's anti-drugs war in a swift visit to the port city of Cartagena.
There was heavy security for the eight-hour visit. Local police arrested two men said to be preparing a small 2 kg bomb not far from a building that Mr Clinton was due to visit. A police spokesman said the device was designed to "cause panic but not huge damage".
In the capital Bogota, 400 miles away, a policeman was killed in clashes with students throwing homemade explosives.
Waving a giant US flag covered with skulls instead of stars, thousands of students and workers, wearing "Uncle Sam" hats and skeleton masks, took part in the protest march to the US embassy in the capital.
It was one of a series of anti-American protests in recent days in which at least 12 people have died.
The protests were organised by the Marxist guerrillas of the Revolutionary Armed Forces of Colombia (FARC), which controls large areas of the country.
Mr Clinton has rejected criticism that the US aid for training anti-drug troops and supplying helicopters is the start of a Vietnam-style intervention in Latin America.
"A condition of this aid is that we are not going to get into a shooting war. This is not Vietnam neither is it Yankee imperialism," he said at a news conference.
Critics, including some from Ireland, say that a military campaign against the drug barons will result in them transferring their operations elsewhere in the region.
The President has also angered human rights groups by releasing aid to the Colombian military without tying it to internal reforms demanded by Congress.
Mr Clinton said yesterday that there must be an end to human rights abuses by the warring factions and that includes the security forces.
He hopes to head off Congressional criticism thanks to the large bipartisan delegation which accompanied him on his visit headed by the Republican Speaker of the House of Representatives, Mr Dennis Hastert. The Secretary of State, Dr Madeleine Albright, and the Attorney General, Ms Janet Reno, were also part of the group.
Mr Clinton, who was accompanied by his daughter, Chelsea, was greeted by Colombia's President, Mr Andres Pastrana, who has emphasised that the US antiterrorist aid is part of the larger $7.5 billion "Plan Colombia". This plan is aimed at persuading peasants to switch from growing coca and poppy for drugs to other crops and to strengthening democratic institutions.
Colombia is the world's leading cocaine exporter and an increasing source for heroin reaching the US.
The 36-year war inside Colombia against the FARC and rightwing paramilitaries has claimed an estimated 35,000 lives.
The FARC commander, Ivan Rios, has said that it would resist what he calls "US aggression".
The US aid will be used to train and equip anti-narcotics battalions. About 60 combat helicopters will be supplied.
But the US aid will also go towards building schools, water systems and roads in the areas where the drug crops are now grown.
Mr Pastrana has been trying to negotiate a peace settlement with the FARC which controls an area in the south of the country about the size of Switzerland.
He has appealed to the FARC to eradicate coca growing in this area
President Clinton toured parts of Cartagena, was briefed on the drugs war and met widows of police officers killed on duty.
He also visited a poor area of the city where the US has funded 20 justice centres where people can get legal aid and advice.