Riyadh (AFP) - A Yemeni rebel strike targeted a desalination plant in the southwestern Saudi province of Jizan, a Riyadh-led military coalition fighting the rebels said Thursday.

The projectile struck near the plant in the Al-Shuqaiq area of Jizan late Wednesday, coalition spokesman Turki al-Maliki was quoted as saying by the official Saudi Press Agency.

It reported no casualties or damage, adding that they were investigating the nature of the projectile.

The coalition will take "firm measures, urgent and timely, to deter this terrorist militia", Maliki said.

Late Wednesday, Yemen's Iran-aligned Huthi rebels said they fired a missile at a power station in Jizan province.

The White House said on Thursday that President Donald Trump had been briefed about reports of a missile strike on Saudi Arabia, without offering details.

Later on Thursday, Maliki said Saudi forces intercepted an unmanned Huthi drone targeting Jizan. The rebels claimed they were targeting Jizan airport, according to the group's Al-Masirah TV.

The rebels, who have faced persistent coalition bombing since March 2015 which has exacted a heavy civilian death toll, have stepped up missile and drone attacks across the border in recent weeks.

Last week, a rebel missile attack on the international airport in the southwestern city of Abha wounded 26 civilians, drawing promises of "stern action" from the coalition.

Human Rights Watch denounced last week's strike as an apparent "war crime", urging the Huthis to immediately stop all attacks on civilian infrastructure in Saudi Arabia.

The attacks come amid heightened regional tensions with Iran, which Saudi Arabia has repeatedly accused of supplying sophisticated weapons to the rebels. Tehran denies the charge.

Saudi state media have reported an intensification of coalition air raids on rebel positions in the northern Yemeni province of Hajjah and the capital Sanaa.

The coalition intervened in support of the Yemeni government in 2015 when President Abedrabbo Mansour Hadi fled into Saudi exile as the rebels closed in on his last remaining territory in and around second city Aden.

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Since then, the conflict has killed tens of thousands of people, many of them civilians, relief agencies say.

It has triggered what the UN describes as the world's worst humanitarian crisis, with more than 24 million Yemenis -- more than two-thirds of the population -- in need of aid.

On Thursday the Saudi campaign in Yemen suffered a double blow as US lawmakers voted to block Trump's arms sales to Riyadh just hours after Britain temporarily suspended similar sales.