A senior United Arab Emirates official said an ultimatum for the United Nations to convince the Iran-aligned Houthi movement to evacuate Yemen's main port of Hodeidah expired on Tuesday night.
The Saudi-led coalition, which the UAE is part of, is gearing up for an assault on Hodeidah, preparing to launch by far the biggest battle of a three-year-old war between an alliance of Arab states and the Houthi movement that controls Yemen's capital Sanaa.
Hodeidah, the only Yemeni port controlled by the Houthis, serves as a lifeline channeling food, medicines and other vital imports to the majority of Yemenis who live in Houthi-ruled territory.
"We gave UN special envoy Martin Griffiths 48 hours to convince the Houthis to withdraw from the port and city of Hodeidah," UAE Minister of State for Foreign Affairs Anwar Gargash told France's Le Figaro newspaper.
"We are awaiting his response. These 48 hours expire during the night of Tuesday and Wednesday."
The United Nations said it was engaged in "intense" shuttle diplomacy between the Houthis and coalition leaders Saudi Arabia and the UAE to avert an all-out attack.
"If the Houthis don't get out of Hodeidah city and the port, the UAE will start a military operation against the rebels in Hodeidah," Gargash was quoted as saying by the French daily.
"Thanks to them controlling the port of Hodeidah, they are getting financing, which allows them to get weapons, weapons such as missiles that are then fired on Saudi Arabia."
Amid the diplomatic efforts to avert a worsening of an already desperate humanitarian crisis in Yemen, French President Emmanuel Macron spoke to Abu Dhabi Crown Prince Mohammed bin Zayed, Macron's office said.
"(He) called for restraint from all the belligerents and to protect civilians," his office said.
France is trying to arrange a humanitarian conference on June 27 co-presided with Saudi Arabia, although it has come under pressure from non-governmental organisations to reconsider given the possible offensive on Hodeidah.