Mohammed Ali al Houthi, the head of the rebels' Supreme Revolutionary Committee, says the pullout started on Saturday at 0700 GMT. But the Yemen government says the rebels are faking withdrawal.
Yemen's Houthi rebels say they have begun a long-delayed withdrawal of their forces from the key port city of Hudaida, following a UN-brokered ceasefire.
Mohammed Ali al Houthi, the head of the rebels' Supreme Revolutionary Committee, says the pullout from Hudaida, as well as Salif and Ras Issa ports started on Saturday at 0700 GMT.
The Houthi-run Al Masirah TV channel said UN observers are monitoring the forces' withdrawal.
The head of the UN operation monitoring the cease-fire, Lt. Gen. Michael Lollesgaard, said on Friday that the Houthi's withdrawal from the three ports marked the first practical step toward realising the ceasefire agreed on in December in Sweden.
He added that the Houthis must commit to fully following through on the redeployment, which is expected to take place over three days.
The rebels also called on the UN on Saturday to press the Saudi-led coalition to implement the Hudaida agreement and take "similar steps."
TRT World's Reagan Des Vignes reports.
Government scepticism over pullout
A senior pro-government official in Yemen accused Houthi rebels of faking the pullout, as a UN source said monitoring of the much-delayed withdrawal in Hudaida province was underway.
"The Houthis are staging a new ploy by handing over the ports of Hodeida [Hudaida], Saleef and Ras Issa to themselves without any monitoring by the United Nations and the government side," governor of Hudaida province Al Hasan Taher told AFP.
Sources close to the Houthis told AFP that the ports were handed over to coastguard personnel who were in charge before the rebels took over almost five years ago.
But Taher contended the Houthis were merely reshuffling personnel.
Meanwhile, the UN has started monitoring this unilateral step.
"The UN hopes soon to be in a position to report to the Security Council on actual movements on the ground," a source told AFP.
The withdrawal of rebel forces is due to be completed by Tuesday, the head of the UN redeployment committee, General Michael Lollesgaard, said in a statement.
The Security Council is due to hear a briefing on Hudaida on Wednesday.