Venezuela's President Nicolas Maduro greets supporters during his closing campaign rally in Caracas, Venezuela May 17, 2018. REUTERS/Carlos Jasso

BOGOTA (Reuters) - President Nicolas Maduro’s socialist government has been giving Venezuelan identification cards to Colombians in order to transport them over the border to vote for him in Sunday’s presidential elections, the Colombian government said on Thursday.

The diplomatic relationship between the neighboring countries has grown increasingly fraught as hundreds of thousands of Venezuelans migrants have fled to Colombia and other countries to escape economic devastation and hunger.

Maduro is likely to win re-election to a six-year term in the contest this weekend, which the opposition is largely boycotting. His main rival is former state governor Henri Falcon, who broke with the opposition to run.

“Through trustworthy intelligence sources we have knowledge of a plan by the Maduro regime, in progress since the end of last year, to give identifications to Colombian citizens and transport them to vote in the May 20 elections,” Colombian President Juan Manuel Santos said in a televised address.

“The plan details the manner, procedures and payments to be made to guarantee the movement of the voters and their vote in favor of Maduro,” said Santos.

The Colombian president did not provide further details about the alleged plot, but said it reaffirmed Colombia’s decision not to recognize the results of Sunday’s vote.

The Colombian military will be increasing patrols along the two countries’ porous 2,220-km (1,380-mile) land border to prevent the movement of illegal voters, Santos added.

The Venezuelan government did not immediately respond to a request for comment.