Republic of Congo has instructed telecommunications firms operating in the country to block service during Sunday's presidential vote.

A letter dated Friday from Raymond Zephirin Mboulou, the interior minister, to the head of local operations for the South African-based firm MTN said all communications including text messages should be blocked on Sunday and Monday for security reasons.

The letter, obtained by The Associated Press on Saturday, refers to a list of numbers that are to continue to receive communications during the two days.

Republic of Congo's longtime President Denis Sassou N'Guesso is facing off against eight opponents Sunday in an election held five months after a referendum removed term and age limits that would have barred him from running. The run-up to October's referendum was marred by violence.