A dispute between Moscow and Minsk over the detention of more than 30 men who Belarus accused of being Russian mercenaries deepened on Saturday, as the two sides contradicted each other about the group’s plans.

The arrests soon before an August 9 presidential election in Belarus could further strain relations between Minsk and its traditional ally Russia, which soured after the neighbours failed to agree on an oil supply contract for this year.

Russia said on Thursday that the men, who it described as employees of a private security firm, had stayed in Belarus after missing their connecting flight to Istanbul.

But Alexander Agafonov, the head of the Belarusian investigative group which is handling the case, said late on Friday that the men had no plans to fly further to Istanbul.

Authorities in Minsk said a day earlier they believe the husband of Opposition presidential candidate Svetlana Tikhanouskaya may have ties to the group, launching a criminal case against him.

Mr. Agafonov told a local television station the men’s had given “contradictory accounts” about the purpose of their stay in Belarus.