A husband and wife were killed as a missile struck a Saudi border region across from war-torn Yemen, official media said on Wednesday.

They died on Tuesday when a missile hit their building in the Jazan region, civil defence Major Yahya al-Qahtani was quoted as saying by the official Saudi Press Agency.

He did not specify whether the missile was fired from across the border.

But the interior ministry late Tuesday said three people were killed when Iran-backed Huthi rebels bombarded Najran city adjacent to Jazan.

The husband and wife lived in Jazan's Al-Harth municipality, where a border guard died last Thursday when a missile hit his patrol vehicle.

The interior ministry did not say if the three other people killed on Tuesday were civilians or troops.

A Saudi-led coalition launched air strikes on anti-government rebels in Yemen on March 26, sparking sporadic border clashes with Saudi forces.

Fighting along the frontier has killed 12 Saudi soldiers and guards but no civilian casualties had previously been reported.

"Three dead after Najran region attacked by mortar rounds and random Katyusha rockets from Yemen territory," the interior ministry said in a tweet sent late Tuesday.

Brigadier General Ahmed al-Assiri told state television that rebel fire hit "hospitals, schools and civilian homes" in Najran city and surroundings.

He said casualties occurred at a field hospital outside the city.

Saudi news channel Al-Ekhbariya showed footage of cars with windows blown out, chunks torn from pavements, a building peppered with shrapnel and one completely charred room with a hole in the ceiling.

Tuesday's assault was the first by the Huthis on an inhabited Saudi town.

It came as leaders of the six Sunni-dominated Gulf Cooperation Council states held a special summit in Riyadh, with French President Francois Hollande in attendance.

The United Nations says at least 1,200 people have been killed in Yemen since March 19, roughly half of them civilians.

The coalition says it has killed hundreds of rebels in northern Yemen.