DUBAI/BEIRUT (REUTERS) - Saudi Arabia's Crown Prince Mohammed bin Salman said on Tuesday (Nov 7) that Iran's supply of rockets to militias in Yemen is an act of "direct military aggression", Saudi state news agency SPA reported.

The supply of rockets to the Iran-allied rebel Houthi movement could "constitute an act of war against the Kingdom," SPA quoted the crown prince as saying in a telephone call with the British Foreign Minister Boris Johnson.

Saudi air defence forces intercepted a ballistic missile they said was fired towards Riyadh on Saturday by the Houthi militia which controls large parts of neighbouring Yemen, including the capital Sanaa, in the country's civil war.

Iran has denied it was behind the missile launch, rejecting the Saudi and US statements condemning Tehran as "destructive and provocative" and "slanders".

In an interview with CNN television on Monday, Saudi Foreign Minister Adel al-Jubeir accused the armed Lebanese Hezbollah group of firing the missile at Riyadh from Houthi-held territory.

"With regards to the missile...that was launched on Saudi territory, it was an Iranian missile launched by Hezbollah from territory occupied by the Houthis in Yemen." He said the missile was similar to one launched in July at Yanbu in Saudi Arabia and was manufactured in Iran, disassembled and smuggled into Yemen, then reassembled by the operatives of the Iranian Revolutionary Guards and Hezbollah, "then it was launched into Saudi Arabia". In reaction to the missile, the Saudi-led military coalition fighting against the Houthi movement in Yemen said on Monday it would close all air, land and sea ports to the Arabian Peninsula country.

The move is likely to deepen a humanitarian crisis in Yemen that according to the United Nations has pushed some seven million people to the brink of famine and left nearly 900,000 infected with cholera.

Saudi Gulf Affairs Minister Thamer al-Sabhan, in an interview with Al-Arabiya TV on Monday, also 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 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.

Hariri cited an assassination plot against him in the statement announcing his resignation, and launched a scathing attack against Iran and Hezbollah for sowing strife in the Arab world.

The crisis has pitched Lebanon back into the forefront of a regional struggle between Saudi Arabia and Iran, which has also played out in Syria, Iraq, Bahrain and Yemen.

There was no immediate comment from the Lebanese government.

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.