U.N. officials say a dozen police officers from Britain, Germany and Sweden have been banned from returning to the U.N. peacekeeping mission in South Sudan after they left during recent fighting without consulting mission chiefs.

U.N. deputy spokesman Farhan Haq told reporters Thursday that their sudden departure affected "the operational capability of the mission and the morale of staff."

He said U.N. peacekeeping has therefore decided "to disinvite" the officers to return to South Sudan.

Recent clashes between opposing army factions loyal to the president and the vice president left hundreds dead.

U.N. peacekeeping spokesman Nick Birnback disputed published reports of an internal memo quoting U.N. officials as questioning if Britain is worthy of being a veto-power on the Security Council after the country withdrew its police officers.