Iraq declared that all ships going to or from Iranian ports in the northern zone of the Persian Gulf were subject to attack. They used F-1 Mirage, Super Etendard, Mig-23, Su-20/22, and Super Frelon helicopters armed with Exocet anti-ship missiles as well as Soviet-made air-to-surface missiles to enforce their threats. Iraq repeatedly bombed Iran's main oil export facility on Kharg Island, causing increasingly heavy damage. As a first response to these attacks, Iran attacked a Kuwaiti tanker carrying Iraqi oil near Bahrain on 13 May 1984, as well as a Saudi tanker in Saudi waters on 16 May. Because Iraq had become landlocked during the course of the war, they had to rely on their Arab allies, primarily Kuwait, to transport their oil. Iran attacked tankers carrying Iraqi oil from Kuwait, later attacking tankers from any Persian Gulf state supporting Iraq. Attacks on ships of noncombatant nations in the Persian Gulf sharply increased thereafter, with both nations attacking oil tankers and merchant ships of neutral nations in an effort to deprive their opponent of trade. The Iranian attacks against Saudi shipping led to Saudi F-15s shooting down a pair of F-4 Phantom II on 5 June 1984.