SANTIAGO, Chile - Colombia's president on Friday criticized Sen. Hillary Clinton's opposition to a free-trade accord between the South American nation and the United States, saying it reflects "an unforgivable lack of understanding" of his country.

Responding to a reporter's question at an Ibero-American summit in Chile, President Alvaro Uribe called the Democratic presidential hopeful's announcement that she will oppose the pact "very serious." He did not say more on the subject.

On Thursday, Clinton said she supports a trade deal with Peru already passed by the House of Representatives, but opposes pacts with South Korea, Panama and Colombia.

"I am very concerned about the history of violence against trade unionists in Colombia," she said in a statement.

Colombia is the world's most violent nation for union workers, with more than 800 killed in the last six years, according to government figures. Another 26 have been killed so far this year.

Uribe, Washington's staunchest ally in Latin America, considers the trade deal his biggest foreign policy achievement. The pact was approved in June by Colombian lawmakers.

The White House also wants the accord, but has yet to send it to Congress amid concerns it might not have the votes to secure passage.

In June, Uribe honored former President Clinton at a New York gala that coincided with a costly lobbying campaign by Colombia to win passage of the trade agreement and ensure the continuation of some $700 million in annual foreign aid. Sen. Clinton was invited but did not attend.