UNITED NATIONS (Reuters) - The head of a United Nations mission tasked with overseeing a peace deal in Yemen’s Hodeidah port city plans to step down next month and will be replaced with a Danish official, U.N. diplomats said on Thursday.

FILE PHOTO: Retired Dutch General Patrick Cammaert, who heads a United Nations advance team tasked with monitoring a ceasefire between the Iranian-aligned Houthi group and Saudi-backed government forces in Yemen's Hodeidah, sits with Houthi officials upon his arrival at Sanaa airport, Yemen December 23, 2018. REUTERS/Khaled Abdullah -/File Photo

Retired Dutch general Patrick Cammaert arrived in Hodeidah late last month to lead an advance team of monitors observing a ceasefire and redeployment of forces agreed by the Iranian-aligned Houthi group and Saudi-backed Yemen government forces.

Diplomats, speaking on condition of anonymity, said the United Nations plans to replace Cammaert next month with Danish Major General Michael Anker Lollesgaard, who led a U.N. peacekeeping mission in Mali in 2015 and 2016.

Lollesgaard - who, like Cammaert, will report to U.N. Yemen envoy Martin Griffiths - will oversee boosting the monitoring mission to up to 75 observers, a move that was authorized by the Security Council earlier this month.

It was not immediately clear why Cammaert was stepping down.

“As far as we know he is only resigning because he said he wouldn’t do it very long,” said a senior U.N. diplomat, speaking on condition of anonymity.

The ceasefire - agreed by the warring parties at talks in Sweden last month - has largely held but sporadic skirmishes have flared. The United Nations has struggled to implement the withdrawal of forces from both sides.

“If anything the ceasefire has held in substance longer than I think we might have thought, but it’s obviously not easy, and it’s very challenging ... because the parties have different interpretations of what was agreed in Stockholm,” said the diplomat.

An armored car in Cammaert’s convoy was hit by a bullet last week as he was leaving a meeting with representatives of the government of Yemen. No-one was injured and the United Nations said it did not know who fired the bullet.

The truce has averted a full-scale assault on Hodeidah, the entry point for the bulk of Yemen’s commercial imports and vital aid supplies. It is a lifeline for millions of Yemenis facing severe hunger in the poorest Arabian Peninsula country.

A military coalition led by neighboring Saudi Arabia intervened in Yemen in 2015 to back government forces. The U.N. and Western countries have criticized the coalition for killing a large number of civilians, including children.

The Gulf states accuse Iran of supplying arms to the Houthis, a charge Tehran and the group deny.