Iran has been forced to disconnect key oil facilities after suffering a malware attack on Sunday, say reports.

The computer virus is believed to have hit the internal computer systems at Iran's oil ministry and its national oil company.

Equipment on the Kharg island and at other Iranian oil plants has been disconnected from the net as a precaution.

Oil production had not been affected by the attack, said the Mehr news agency.

However, the attack is believed to have been responsible for knocking offline the websites of the Iranian oil ministry and national oil company.

The Ministry website was back in action on Monday but the oil company site has remained unreachable.