The United Nations envoy for Yemen has held talks with the country's internationally recognised president in the Saudi capital, Riyadh, amid efforts to convince the warring sides to implement a fragile truce in the lifeline port city of Hodeidah.

The meeting on Tuesday between Martin Griffiths and Abd-Rabbu Mansour Hadi came days after the UN diplomat saw Houthi rebels in their stronghold, Yemen's capital, Sanaa.

Hadi, who is backed by a Saudi-UAE-led coalition, expressed his "support for the efforts and work" of Griffiths at the talks, according to Saba news agency.

Abdullah al-Alimi, the head of the president's office, wrote on Twitter that Hadi remained committed to the ceasefire accord that was agreed upon in Sweden last month and stood ready to open up "all humanitarian access".

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Under the terms of the UN-brokered truce deal, the Houthis were expected to hand over control of the ports of Hodeidah, Saleef and Ras Isa to "local authorities in accordance with Yemen law".

However, both sides have been in disagreement over the wording of the agreement.

The government has interpreted it to mean that the port should be handed over to the officials who ran the facility before the Houthis seized the Hodeidah city in late 2014. The rebels, however, insist the deal refers to the officials currently running the port, who are their allies.

There have also been disagreements over the redeployment of forces.

Under the deal, the Houthis and forces loyal to the Yemeni government were expected to withdraw from Hodeidah, with a ceasefire expected to come into effect in the entire governorate.

However, both sides have accused each other of violating the truce, with the sound of missiles and automatic gunfire, a near-daily occurrence for the thousands of civilians who still reside in the city.

Griffiths is expected to brief the UN Security Council on Wednesday on the state of the ceasefire deal and his latest efforts to end Yemen's nearly four-year war.

He is looking to push on with steps agreed by the warring sides in Sweden, including the redeployment of rival forces from Hodeidah. He is also hoping to bring the sides together again for a new round of peace talks later this month.

Meanwhile, UN Secretary-General Antonio Guterres has reportedly asked the Security Council to approve the deployment of up to 75 observers to Hodeidah for six months to monitor the ceasefire and redeployment of forces.

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The 15-member council will need to take action on Guterres' request by about January 20, when a 30-day authorisation for an advance monitoring team led by retired Dutch General Patrick Cammaert expires. It was not immediately clear how many monitors were currently on the ground with Cammaert. The UN has said the monitors are not uniformed or armed.

The Security Council had asked Guterres to recommend - by the end of last month - a larger monitoring team. Diplomats said Britain was working on a draft resolution to approve Guterres' proposal, but had not yet circulated it to council members.

In his December 31 proposal to the council, seen by Reuters news agency, Guterres described the proposed 75-strong team as "a nimble presence" to monitor compliance of the deal and establish and assess facts and conditions on the ground.

"Appropriate resources and assets will also be required to ensure the safety and security of UN personnel, including armoured vehicles, communications infrastructure, aircraft and appropriate medical support," Guterres wrote.

"Such resources will be a pre-requisite for the effective launch and sustainment of the proposed mission," he said.

Hodeidah was for months the main front line in the Yemen war after the Saudi-UAE-backed pro-government forces launched an offensive to capture it in June.

The Red Sea port is the key point of entry for humanitarian aid and supplies to Yemen, where millions are on the brink of famine as the war has continued on.

Yemen has been wracked by violence since 2014 when the Houthis stormed south from their stronghold of Saada and overran much of the country, including the capital Sanaa where they toppled Hadi's unpopular government.

The conflict escalated in 2015 when Saudi Arabia and the UAE, who accuse the Houthis of being Iranian proxies, launched a military coalition that began air attacks against Houthi positions in an attempt to reinstate Hadi.

With logistical support from the US, the coalition has carried out more than 18,000 raids, with schools, hospitals and mosques frequently targeted.

According to recent estimates, as many as 85,000 children may have died of hunger since the coalition's intervention.

The conflict has unleashed the world's worst humanitarian crisis, according to the UN, which says 14 million Yemenis are on the brink of famine.