Russian hackers were behind a fake news report in Qatar's state media that helped stir the Gulf nation's current diplomatic crisis, US investigators reportedly believe.

The state-run Qatar News Agency has been offline since a supposed hack in May that reignited tensions between the gas-rich nation and its Gulf Arab neighbours over its alleged support of Islamist groups.

After an FBI team was sent to Doha to help the Qatari government investigate, US officials have intelligence indicating Russian hackers were behind the intrusion, according to CNN.

The Kremlin responded by saying there was "zero" proof that Russian hackers were involved, the Interfax news agency reported.

The supposedly fake report, published last month, quoted Emir Tamim bin Hamad al-Thani, the Emir of Qatar, on a number of sensitive regional issues and Doha’s relationship with Donald Trump. Its publication is thought to have contributed to tensions between neighbouring countries.

Mr Thani was quoted as saying “there is no wisdom in harbouring hostility towards Iran” and that his relationship with the Trump administration was “tense” despite a positive meeting between the two leaders in Riyadh, the Saudi Arabian capital.

Qatar’s ties to Israel were “good”, the story quoted the sovereign as saying, and that he hoped to help broker a peace deal in the Arab-Israeli conflict. It attributed to the ruler positive statements about Lebanese militant group Hezbollah and Gaza-based extremist organisation Hamas.

Qatar's foreign minister, Sheikh Mohammed Bin Abdulrahman al-Thani, told CNN: “Whatever has been thrown as an accusation is all based on misinformation.

“It was started based on fabricated news, being wedged and being inserted in our national news agency which was hacked and proved by the FBI.”

According to the broadcaster it was not clear whether the hack had been traced to criminals or official Russian organisations.

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The biggest diplomatic crisis in the Persian Gulf since the 1991 US-led war with Iraq pits several nations against Qatar, home to some 10,000 American troops and a major US military base.

Saudi Arabia broke diplomatic relations and all land sea and air contacts with Qatar on Monday, saying the move was necessary to protect the kingdom from what it described as terrorism and extremism.

Bahrain, Egypt and the United Arab Emirate have also cut ties, as have the internationally recognised governments of Yemen, Libya and The Maldives.