Saudi Arabia said on Monday that Lebanon had declared war against it because of what it described as “aggression” against the Kingdom by the Iran-backed Hezbollah terrorist group.

Saudi Gulf affairs minister Thamer al-Sabhan, speaking in an interview with Al-Arabiya TV and quoted by Reuters, said the Lebanese government would "be dealt with as a government declaring war on Saudi Arabia."

Sabhan said this message had been delivered to the Saudi-allied Lebanese politician Saad al-Hariri, who declared his resignation as the country's prime minister on Saturday in a broadcast from Saudi Arabia.

Hezbollah's acts of "aggression" on the Kingdom "were considered acts of a declaration of war against Saudi Arabia by Lebanon and by the Lebanese Party of the Devil", he added, according to Reuters.

Hariri cited the "grip" of Hezbollah and Iran on the country, and also said he feared for his life, when he announced his resignation.

Hezbollah was a member of Hariri's coalition but has in the past been blamed for the 2005 assassination of Hariri's father, Rafik al-Hariri, who also held the post of Lebanese Prime Minister.

Hezbollah leader Hassan Nasrallah said on Sunday that the resignation of Hariri had been "imposed" by Saudi Arabia and it was “not his wish and not his decision" to quit.

There was no immediate comment from the Lebanese government to Sabhan's remarks..

Earlier on Monday, President Michel Aoun, a political ally of Hezbollah, appealed for national unity following Hariri's resignation which toppled a coalition government that included Hezbollah and plunged Lebanon into political crisis.

Parliament Speaker Nabih Berri, another political ally of Hezbollah, said in a televised statement after meeting Aoun it was too early to talk about forming a new government.

Shiite Iran and Sunni Saudi Arabia have a historic rivalry in the Middle East. Saudi Arabia has repeatedly called on Iran to stop its “meddling” in the affairs of the kingdom's neighbors.

Iran has fired back, accusing Saudi Arabia of trying to “drag the entire region into confrontation”.