"There is no right to enforce unilateral sanctions through an armed blockade," the UN experts said in a joint statement.

A blockade is a prohibited use of military force against another country under the UN Charter, they added.

"It is such a serious use of force that it is also expressly recognised as illegal armed aggression under the General Assembly's 1974 Definition of Aggression," they said.

"As such, it is an armed attack under article 51 of the Charter -- in principle giving the victim state a right of self-defence."