The UAE - a key member of the Saudi-led coalition fighting in Yemen - has pulled troops from the southern port of Aden and its western coast where it has built up and armed local forces leading the battle against the Houthi rebels, diplomats told Reuters news agency on condition of anonymity.

Three diplomats said Abu Dhabi preferred to have its forces and equipment on hand should tension between the United States and Iran escalate further, after attacks on oil tankers in the Gulf and Tehran's downing of an American drone last week.

It was unclear exactly how many troops had been drawn down.

A western diplomat said the UAE withdrew "a lot" of forces from Yemen over the last three weeks.

"It is true that there have been some troop movements ... but it is not a redeployment from Yemen," a senior Emirati official was quoted as saying. He added the UAE remains fully committed to the military coalition and "will not leave a vacuum" in Yemen.

The Saudi-Emirati alliance intervened in Yemen in 2015 to try to restore the government that was overthrown by the Houthis.

Asked whether tensions with Iran were behind the move, the Emirati official said the troop movement was related to a ceasefire in Yemen's main port city of Hodeidah, now held by the Houthis, under a UN-led peace pact reached last December.

"This is a natural progression," the official said, reiterating the UAE's support for UN efforts to implement the Hodeidah deal.

Hodeidah became the focus of the war last year when the coalition tried to seize the port, the Houthis' main supply line.

Under the deal, which has yet to be fully implemented, both the Houthis and pro-coalition forces would withdraw from Hodeidah.

Tankers targeted

Two diplomats said progress on Hodeidah made it easier for the UAE to scale back its military presence in Yemen to reinforce defences at home in the wake of the attacks on four oil tankers off the UAE coast in May, which were followed by attacks on two more vessels in the Gulf of Oman a few weeks later.

Washington and Riyadh have publicly blamed Iran for the mysterious explosions, allegations Tehran has vehemently denied.

The US is in talks with allies for a global coalition to protect vital oil-shipping lanes in and near the Strait of Hormuz - through which 20 percent of the world's oil supply passes.

The Houthis have stepped up missile and drone attacks on Saudi cities, further heightening tensions.

The Yemen conflict, which has killed tens of thousands of people and pushed the country to the verge of famine, is largely seen as a proxy war between Saudi Arabia and Iran, which publicly supports the rebels.