Mexican President Felipe Calderon was warned during the early years of his administration of a credible threat to assassinate him while he was in the presidential jet, Mexican media reported on Sunday.

According to reports in major newspapers, Calderon said on Saturday that security advisers told him before a trip within Mexico that they had information about the assassination attempt, although he took the plane anyway.

The trip went smoothly, but Calderon was concerned enough to record a video message for his children before the trip in case he was killed, the reports quoted him as saying. Calderon has spoken before about threats he received after launching a war against drug cartels, but never in any detail.

"Before the trip I recorded a message for my children in which I assured them that in case something happened to me, they should be sure of knowing that their father was carrying out work which he felt to be necessary," Universal newspaper quoted him as saying during a private party for his 50th birthday.

The threat was relayed to Calderon by the head of the presidential guard, General Jesus Castillo, according to Excelsior newspaper.

"They had uncovered information that they wanted to make an attempt against the presidential plane. He told me that this was not the first time that there had been threats against the president but this time they were credible," Calderon said, according to Excelsior.

The president's office had no immediate comment on the latest reports, which did not say who may have been behind the assassination threat.

Excelsior said the assassination threat may have taken place in 2008. However, another daily newspaper, Milenio, said the threat took place in 2007.

In March 2007, Calderon told Reuters he had received threats to his life. "We have received a lot of threats and will no doubt receive more," he said in the 2007 interview. "We don't know if they are real or false."

Since taking office in December 2006, Calderon has led a national offensive against drug cartels, in which more than 55,000 people have died and security forces have arrested or shot dead major kingpins and made record seizures of narcotics.

Cartel gunmen have struck back by assassinating some senior law enforcement officials, including the acting head of the federal police in 2008, and are also alleged to have murdered more than 3,000 other police officers, soldiers, judges and mayors during Calderon's administration.

In December, Calderon will be succeeded by Enrique Pena Nieto of the opposition Institutional Revolutionary Party, or PRI, which led Mexico for most of the 20th century.

The president told guests at his birthday party, who included top businessmen and senior politicians, that when he leaves office he planned to write books, attend conferences and "do whatever I like."

Newspaper reports have said he is in discussions with several U.S. universities about positions outside Mexico, but the universities have declined to comment.