Yemen's Saudi-backed government has announced a major military operation to retake territory from the Iran-backed Houthis.

It comes after an exchange of strikes between the Houthis and the Saudi-led coalition in recent days. On Sunday, the Houthis said they had struck sites belonging to Saudi national oil company Aramco.

The group said the attack was in response to what it described as 50 Saudi-led coalition air and missile strikes in Yemen in 12 hours. Saudi Arabia has yet to comment.

The conflict escalated in September, when the Houthis seized the country's entire Red Sea coast, including the vital shipping lane of the Bab al-Mandab Strait, further disrupting global oil supplies.

Yemen's capital, Sanaa, which has been held by the Houthis for more than a decade, has come under sustained attack as government forces try to weaken the group's military capabilities.

Attacks on the Houthis have also spread across Yemen, including to the Saada region, the group's northern heartland.

On Sunday, Yemeni President Rashad al-Alimi said in a televised address: "Today, I announce the start of military operations to retake the remaining territory of the republic and extend the authority of the state and its institutions across the entire national territory."

But it is not yet clear whether this represents a new phase in the conflict.

The frontline in Yemen remains focused around the key city of Taiz, which is still controlled by the internationally recognised government.

The Houthis are engaged in a fierce battle with government forces for control of the region, as they seek to secure coastal areas and, by extension, the Bab al-Mandab Strait.

On Sunday, the Houthis cut a vital supply route linking Taiz with Aden, the interim capital of the Yemeni government, AFP news agency reports.

Citing three Yemeni military sources, AFP also reports that the Houthis now control the area and supply route, effectively encircling Taiz.

"They've achieved the military objective of isolating Taiz from Aden, even if they haven't fully taken control of it," Farea Al-Muslimi, a research fellow at the Chatham House think tank, told AFP.

Away from Yemen, the Houthis are also trying to hurt the Saudis with an attack aimed at the country's economic lifeblood – oil.

On Sunday, Yemen's Houthi military spokesman Yahya Saree said the group had launched a ballistic missile and drone attack on Aramco sites in the capital, Riyadh, and the oil-rich Khurais area in the kingdom's east.

"Both operations successfully achieved their objectives," the spokesman said in a statement. "The strikes were precise, causing large fires at the targeted sites."

It is not the first time the group has said it has hit Saudi oil sites. Saudi Arabia has yet to comment on Sunday's claimed attack, but has previously dismissed some claims as misleading, mocking the Houthis for "chasing imaginary victories".

But it has once again shown the price Saudi Arabia – and, as a consequence, the global economy – could pay if it launched a new all-out war against the Houthis.

In retaliation, Saudi Arabia has also been striking Houthi targets, according to the Houthi-run Al-Masirah TV channel. It said at least two people had been wounded in strikes on Sunday.

On Saturday, Yemen's government also said its forces had hit Houthi targets across the country, including in Sanaa, Saada and the group's positions near Taiz in the south-west.

Yemen is one of the poorest countries in the world and remains gripped by a vast humanitarian crisis.

A war erupted in 2014, when the Houthis seized the capital, Sanaa, from the Saudi-backed government, before going on to take control of swathes of the country's north.

Riyadh intervened in the war the following year, leading an international coalition.

After several years of relative calm, the war reignited in July amid the widening conflict in the Middle East.

The Houthis have launched a blockade of Saudi energy exports, which have already been squeezed by Iran's closure of the Strait of Hormuz.