The unrest in Yemen is edging towards a civil war, as rival factions vie for control and Islamist militants take advantage of the chaos to gain ground.

Here are some of the facts in the ongoing saga:

Who are the main rivals?

The main conflict is between the southern-based faction led by President Abedrabbo Mansour Hadi, which includes loyalists from the police and military as well as armed militia, and the Houthi movement comprised of minority Shi'ite rebels that have advanced from its base in the north.

The forces allied with the Houthis include members of the former central security force, a unit seen as loyal to former president Ali Abdullah Saleh, who was ousted in 2012 and has been accused of working with the Houthis to restore his influence. The Houthis also count Iran as an ally.

Who are the other groups adding to the fray?

Yemen is home to Al-Qaeda in the Arabian Peninsula (AQAP), an arm of Al-Qaeda that is one of the most active arms, which has carried out attacks abroad.

AQAP opposes both Mr Hadi, an ally in the fight against Al-Qaeda, and the Houthis, who are at war with them. AQAP at one point captured a southern city, killing about 20 soldiers before being driven out by the army.

A Yemen affiliate of the Islamic State in Iraq and Syria (ISIS) has also emerged, and is also seeking to exploit the chaos gripping the country. To complicate things further, the ISIS arm is seeking to siphon support from AQAP, analysts say.

Suicide bombings last Friday at two mosques frequented by members of the Houthis killed 142 people and wounded 351. ISIS has claimed responsibility for them, warning that it was "the tip of the iceberg".

How did the conflict escalate?

The Houthis, who were continually strengthening their power last year, finally stormed the capital Sanaa last September, seizing the state news agency and television station. They took the presidential palace in January, placing Mr Hadi under house arrest, leading to his resignation and that of the prime minister and Cabinet, and effectively placing the country under Houthi control.

But the Sunnis and southern leaders have not recognised the governance of the Houthis, meaning there is potential for further chaos.

Mr Hadi escaped to the southern city of Aden and has temporarily based the government there.

Why does the crisis matter to the rest of the world?

Yemen is located at a strategically important waterway that much of the world's oil shipments pass through. If the Houthis take over the country, it could threaten free passage through the strait.

As the country edges towards civil war, it will also become more unstable, fomenting attacks by militants on global targets, especially Western ones.

Mr Hadi has been a key ally of the West as it fights against AQAP, considered the most dangerous branch of Al-Qaeda. His ouster will pose difficulties for the anti-AQAP campaign.

Finally, the region will also become more unstable as Shi'ite-led Iran is seen as backing the Houthis, while Sunni-led Saudi Arabia supports Mr Hadi. The conflict in Yemen is seen as part of a wider power struggle between Iran and Saudi Arabia

Sources: BBC, Reuters, Agence France-Presse, Straits Times archives