Only three sub-groups within the Trilateral Contact Group for Ukraine will meet in Minsk on Tuesday ahead of the Contact Group's meeting, a source in the group organizing these talks told Interfax.

"We have no confirmation that the sub-group for security will meet today. Three sub-groups, not all four, are expected to meet," he said.

According to earlier news reports, all four sub-groups of the Trilateral Contact Group for Ukraine were expected to hold their meetings in Minsk on Tuesday.