BOGOTA (Reuters) - Colombia’s former President Alvaro Uribe on Wednesday accused President Juan Manuel Santos and Britain’s MI6 spy agency of participating in a plot against him, a day after resigning his Senate seat to face a bribery and fraud investigation by the Supreme Court.

FILE PHOTO: Colombia's former president Alvaro Uribe Velez speaks to the news media after casting his vote at a polling station, during the presidential election in Bogota, Colombia May 27, 2018. REUTERS/Carlos Garcia Rawlins/File Photo

Uribe, a mentor of Colombia’s incoming President Ivan Duque, is under investigation by the court over allegations he made false accusations and tampered with witnesses in a case he himself started by making similar accusations against a leftist senator.

Known for a hardline military crackdown on Marxist guerrillas during his 2002-2010 government, Uribe cited on Twitter what he said were claims that recordings in the case were made by MI6, Britain’s Secret Intelligence Service.

“There are repeated accusations that the recordings were made by the British agency MI6, friends of Juan Manuel Santos. Foreign authorities in a ruse against me,” Uribe said.

He did not specify exactly which recordings he was referring to or the source of the accusations. But in a statement on Tuesday, the Supreme Court referenced intercepted phone calls between a lawyer and a former official that it said had plotted to undermine the case against Uribe.

A spokeswoman for Britain’s Foreign Office declined to comment on Uribe’s tweet. MI6, which is accountable to British Foreign Secretary Jeremy Hunt, did not respond to calls requesting comment.

Uribe had originally tweeted it was MI5, Britain’s domestic intelligence service, which was involved, before correcting himself.

A spokeswoman for President Santos declined to comment. Santos was once a close ally of Uribe’s until they had a bitter falling out over a peace process with Marxist rebels that resulted in a 2016 deal signed by Santos to end their five-decade uprising.

FIRST PRESIDENT TO TESTIFY

Uribe resigned his Senate seat on Tuesday after the Supreme Court asked him to testify in the criminal case, which could result in jail time. It is the first time that the tribunal, which is charged with investigating criminal allegations against lawmakers, has called a former president to testify.

The 66-year-old is seen as the power behind the throne of Duque, 41, who won last month’s presidential election as the candidate for Uribe’s right-wing Democratic Center party.

Uribe’s exit from the Senate just two weeks before Duque’sAug. 7 inauguration could throw the new government into disarray. It will also remove from Congress a vocal critic of the peace deal who had called for tougher treatment of former FARC rebels.

The case that spurred the Supreme Court investigation began in 2012, when Uribe accused leftist lawmaker Ivan Cepeda of orchestrating a plot to falsely link him to right-wing paramilitary groups. Uribe denies any such ties.

But in February the Supreme Court said Cepeda had collected information from former members of paramilitary groups in the course of his Senate work, and that he had not paid or pressured them. Instead, the court said, it was Uribe who was at fault.

The activities continued even after the February ruling, the court said in its Tuesday statement.

Cepeda hailed the Supreme Court’s decision to press Uribe to testify.

“This decision marks a historic milestone in the judicial and political life of nation,” he told Reuters. “Uribe was considered untouchable and all powerful until yesterday. This marks a very important precedent.”

Uribe’s lawyer, Jaime Granados, could not be reached for comment. The former president said on Twitter on Tuesday that his lawyers would not make any statements.

Uribe and his family have long been accused of paramilitary involvement by the opposition, but previous investigations have borne little fruit. The family has also denied any such links.

Paramilitary groups in Colombia - originally funded by landowners eager to protect themselves from rebel fighters - became dreaded death squads linked to rural massacres, drug trafficking and sexual violence.

The demobilization of a major paramilitary group during Uribe’s term in office was widely criticized as ineffective. The 50-year conflict in Colombia has killed more than 220,000 people.