Saudi Arabia launched air strikes on Houthi rebels in Yemen on Thursday, forging a coalition of more than 10 countries to defend embattled President Abd-rabbu Mansour Hadi.

Here are the key dates in Yemen since the Shiite Huthis overran the capital in September 2014:

September 21

Rebels seize government headquarters, state radio and military sites in Sanaa, apparently aided by part of the state apparatus, after several days of fighting that killed more than 270 people.

Rival groups sign a UN-brokered peace deal stipulating a Houthi withdrawal from the capital and formation of a new government.

October 9

Al-Qaeda, which has declared war on the Houthis, claims an attack in Sanaa in which 47 are killed.

October 14

The Huthis seize the Red Sea port of Hodeida, 230 kilometres (143 miles) west of Sanaa, then move towards the centre without opposition from government forces. They capture territory in Dhamar, Ibb and Baida provinces but face fierce resistance from Al-Qaeda and its tribal allies.

January 20

Houthis attack Hadi's residence and seize the presidential palace, and the president and prime minister resign two days later.

February 6

The rebels announce they have dissolved parliament and installed a presidential council to run the country. The United States and Gulf monarchies accuse Iran of backing the Houthis. In the south and southeast, authorities reject what they brand a coup attempt.

February 21

Hadi flees south to Aden after escaping from weeks under house arrest and urges the international community to "reject the coup," rescinding his resignation and subsequently declaring Aden the temporary capital.

March 19

Clashes in which at least 11 are killed force the closure of the international airport in Aden and Hadi is moved to a more secure location after an air raid on the presidential palace there.

March 22

The Houthis advance southwards, seizing the airport and a nearby military base in Taez, 180 kilometres (110 miles) north of Aden and a strategic entry point to Hadi's stronghold.

Houthi leader Abdelmalek al-Huthi says the rebels have moved south to combat Al-Qaeda and the Islamic State group, days after IS claimed suicide bombings which killed at least 142 people at Shiite mosques in Sanaa.

March 25

Hadi is again moved as rebel forces bear down on Aden, capturing a major airbase nearby just days after US military personnel were evacuated from it.

The Houthis advance to just three kilometres (nearly two miles) from Huta, the capital of Lahj province adjacent to Aden.

A warplane targets Hadi's residential complex in Aden but hits an abandoned building, and operations are again suspended at the city's international airport.

March 26

Saudi Arabia bombs the rebels and says it has assembled a coalition of more than 10 countries, including five Gulf monarchies, for a military operation to defend Hadi's government.

The United States says it will provide logistical support and intelligence to the coalition. Iran condemns the Saudi intervention as a "dangerous step".