The warning came after the country's president declared a state of emergency and imposed a night curfew amid escalating tension ahead of polls, scheduled to take place on January 22.

"The United Nations appreciates the traditional role played by the Bangladesh armed forces in support of previous fully contested elections through the maintenance of law and order," said UN resident coordinator Renata Lok Dessallien in a statement.

"However, should the 22 January parliamentary elections proceed without participation of all major political parties, deployment of the armed forces in support of the election process raises questions. This may have implications for Bangladesh's future role in peacekeeping operations," she added.

The Awami League and its allies are boycotting the elections, demanding a total overhaul of the voter list and a swathe of other reforms.