SANAA - A humanitarian group has warned that a ceasefire agreed in Yemen's key port city of Hodeidah is on the verge of collapsing, as a retired Dutch general in charge of the truce stepped down from his role.

The US-based International Rescue Committee said on Tuesday that recent clashes in the city between Houthi rebels who control it and pro-government forces backed by a Saudi-led coalition have increased dramatically since last week.

"In recent days, with clashes erupting inside Hodeidah and both parties accusing each other of violations, the agreement is increasingly in peril," Frank McManus of the group said.

The developments threaten to unravel a ceasefire and prisoner swap signed in December, the group said, urging the international community to step up pressure on the warring parties to stick to their commitments.

The warning comes a day after the United Nations envoy for Yemen urged warring sides to withdraw their troops from the city - a lifeline for millions of Yemenis facing starvation.

Martin Griffith on Monday said that the expected timeline for the truce and the prisoner swap has been pushed back.(FA)