Colombia's President Alvaro Uribe has been sworn into office for a second term as tens of thousands of police patrolled the capital, Bogota.
Uribe has taken a hard line against terrorism and drug trafficking
Before presidents and officials from more than 20 countries, he pledged to seek peace with left-wing rebels and improve the country's economy.
The ceremony took place amid tight security with tanks on the streets and military helicopters overhead.
Officials feared a repeat of his 2002 inauguration, which came under attack.
Rebels from the Revolutionary Armed Forces of Colombia (Farc) fired a barrage of mortars at the presidential palace, killing at least 20 people in a poor neighbourhood a few streets away.
The group had killed more than 20 security officers in the past week. Police said they deactivated a car bomb outside Bogota on Monday.
In his inaugural speech, President Uribe highlighted the successes of his last four years and set out his plans for his next term.
Security forces are a visible presence in Bogota
"We strived without fear in our actions to secure peace," he told Congress.
"Fear will not stop us negotiating. I confess my concern is something else - the risk of failing to get peace and slipping back in security."
The ceremony was attended by 11 South American heads of state as well as dignitaries from other nations.
Increased security in Bogota included army and police checkpoints on the outskirts of the city, snipers positioned on rooftops around the presidential palace and a ban on alcohol consumption.
President Uribe, an ally of Washington, goes into his second term in office amid high expectations, says the BBC's Jeremy McDermott.
He has won praise for his relentless offensives against Marxist guerrillas and a generous amnesty law for right-win paramilitaries over the last four years.
But there is a feeling that he has failed to come close to defeating the rebels and the Colombian public has made it clear it wants more talk and less war in the next four years, our correspondent adds.
Tens of thousands of civilians have been killed in decades of fighting among rebels, right-wing paramilitaries and state forces.
President Uribe also pledged to tackle Colombia's social problems, promising to improve education, health and housing for people while balancing free-market economic policies.
Half of Colombians live below the poverty line, and 13 million have no access to any form of pension.