A nephew of Yemen's ex-strongman Ali Abdullah Saleh who commanded the presidential guard stepped down on Thursday after rejecting for a whole month a decision to sack him, the UN's envoy said.

"I witnessed the handing over of the command of the Third Brigade from General Tariq Mohammed Abdullah Saleh to Abdulrahman al-Halili, who was appointed by President Abdrabuh Mansur Hadi," Jamal Benomar told reporters.

"This measure takes place based on orders by Hadi and I am confident that the president will lead the country towards the shore of safety," he said.

"The time has come for Yemenis to concentrate on ending divisions within the army and on security and stability," said Benomar, who played a major role in convincing the country's former leader to step down in February after a year-long uprising.

A source close to Benomar told AFP that the ousted chief of the presidential guard rejected Hadi's decision to give him command of the 37th battalion of the Republican Guard, which is based in the southeastern province of Hadramawt.

On April 14, former air force commander General Mohammed Saleh al-Ahmar -- a half brother of Saleh -- also agreed to leave the post he held for nearly three decades, after refusing to quit for weeks.

Rejecting the general's dismissal, Ahmar loyalists laid siege to Sanaa's airport and forced its closure for a day after threatening to shoot down planes.

The airport was reopened after international and regional powers voiced support for Hadi, who must restructure the army based on a Gulf-brokered deal that Yemen's political parties have agreed upon.

The Third Brigade has more than 200 tanks and is in charge of protecting the capital Sanaa from all directions.

Diplomatic sources told AFP that General Tariq relented to pressures by Western mediators who threatened to impose sanctions on Saleh and his nephew.

The US ambassador in Sanaa, Gerald M. Feierstein, openly warned last month that the international community could take steps against members of the former regime if Hadi's orders were not implemented.

Benomar will present a report on the situation in Yemen at the UN Security Council on May 17, sources close to him said.

Hadi took power in February after Saleh, who ruled the country for more than three decades, signed the power transfer deal under which he quit in return for immunity from prosecution.

But Hadi, supported by the United States and Yemen's Gulf neighbours, has been facing mounting challenges, with spiralling Al-Qaeda attacks against security forces and his predecessor's lingering influence in the country.

Saleh's son Ahmed still heads the elite Republican Guard, while another nephew, Yehya, commands central security services.