Saudi air strikes on Shia rebels in Yemen have triggered a furious reaction from regional rival Iran, with top officials warning that military action could spill into other countries.

Saudi Arabia said that a coalition consisting of 10 countries, including members of the Gulf Cooperation Council (GCC), had begun air strikes at 2am local time on Thursday, targeting Houthi positions in the capital, Sanaa.

According to Al Jazeera sources, the strikes carried out by 100 jets from Saudi and its coalition, have destroyed Iranian-made missile launchers in the capital Sanaa. The operation has been dubbed, "Decisive Storm."

Houthi military barracks and air bases controlled by the rebels were also reportedly destroyed, Fayez al-Duweiri, a retired Jordanian general and defence analyst, told Al Jazeera.

The Houthi-run health ministry in Sanaa said that at least 18 civilians were killed and 24 others were wounded in the Saudi-led attacks on the capital.

The bombing of the Houthis, who are said to be backed by Iran - a charge Tehran denies - came after several weeks of warnings that Yemen was descending into civil war.

Saudi Arabia said it had launched the bombing raids to reinstate what it called the legitimate government of President Abd-Rabbu Mansour Hadi, who has been holed up in the main southern city of Aden since fleeing rebel-controlled Sanaa.

The Houthis and their allies within the armed forces had been closing in on Hadi's last bastion, Aden.

Iranian Foreign Minister Mohammad Javad Zarif said the air strikes would lead only to greater loss of life.

"Military action from outside of Yemen against its territorial integrity and its people will have no other result than more bloodshed and more deaths," he told the Iranian-owned Al-Alam television channel.

He also called for an "urgent dialogue" among the Yemeni factions "without external interference".

Speaking to Al Jazeera from Sanaa, Houthi spokesman Mohammed al-Bukhaiti called the military action a declaration of war on Yemen, adding that reports alleging a Houthi leader, Mohamed Ali al-Houthi, had been injured were false.

Meanwhile, thousands of pro-Houthi protesters gathered in Sanaa on Thursday to condemn the Saudi-led air strikes. In the city of Taiz, supporters of President Hadi organised a rival protest.

Sanaa targeted

Huge explosions were heard in Sanaa as strikes hit an air base at the capital's airport and other locations in the city, an AFP correspondent reported.

Strikes were also reported on targets in the Malaheez and Hafr Sufyan regions of Saada province, a main Houthi stronghold on the border with Saudi Arabia.

The United Arab Emirates is participating with 30 jets, Bahrain with 12, Qatar with 10, Morocco and Jordan both with six, while Sudan offered three planes, officials said.

An Egyptian official told the AFP news agency that Egypt would also take part. Saudi Arabia said that another four Muslim countries including Pakistan wanted to participate in the military coalition.

Kuwait's defence ministry announced it was sending three squadrons of its F-18 Super Hornet aircraft to Saudi's King Abdulaziz airbase in Dhahran to take part in the offensive.

Four Egyptian war ships also entered the Suez Canal on Thursday en route to the Gulf of Aden after Cairo pledged military support for the campaign, canal officials said.

The officials said the ships will take part in operations "to secure" the strategic waters that control southern access to the Suez Canal.

Pakistan, which has longstanding ties to Saudi Arabia, was examining a request from Riyadh to join the coalition, Islamabad said.

In a statement following the strikes, the White House said that the US was coordinating military and intelligence support with the Saudis but not taking part directly in the strikes.

The European Union, however, opposed the strikes with the EU High Representative and Vice President Federica Mogherini saying the operation "dramatically worsened the already fragile situation" and "risk having serious regional consequences".

"I'm convinced that military action is not a solution," she said, calling for an immediate return to negotiations to resolve the conflict.