ADEN (Reuters) - Seven supporters of President Abd-Rabbu Mansour Hadi were killed on Tuesday by friendly fire from a Saudi-led air strike in north Yemen, tribal sources said, as pro-Hadi forces converged on Marib in preparation to attack Houthi fighters in the region.
In the southern port city of Aden, unidentified gunmen on motorcycles shot dead two leaders of a local force allied with Hadi in separate attacks on Monday, regional officials said.
Saudi-led forces have been waging an air campaign against the Iran-allied Houthis since March to try to halt the Zaydi Shi'ite group's expansion and restore the exiled Hadi to power.
Tribal sources said two members of a local force allied with Hadi were also wounded when Saudi-led jets targeted them by mistake in an area known as al-Khazzan, east of the capital Sanaa, during a clash with Houthi fighters.
Hadi supporters had been reinforcing local tribal fighters with newly-trained recruits and armored vehicles supplied by the Saudi-led coalition in what regional media had said were preparations for an assault to retake Sanaa from the Houthis.
Hadi supporters, who had been on the retreat since the Houthis seized Sanaa a year ago, have made gains in recent weeks with Saudi-led support, capturing Aden and advancing on the strategic southwestern city of Taiz.
But the United Nations says the fighting has often targeted civilians.
In a Geneva, the United Nations said on Tuesday that 95 civilians had been killed in the past two weeks in Taiz, where a collapse in health care services and an outbreak of dengue fever are compounding a dire humanitarian situation.
"We are alarmed by the steep increase in the number of civil casualties in Taiz in recent weeks," U.N. human rights spokeswoman Cecile Pouilly told a news briefing.
Taiz, Yemen's third-largest city, has become the latest front line in a five-month war between Houthi militiamen from the north and supporters of Yemen's exiled government, which is backed by the West and Saudi Arabia. [IDn:L5N1173AJ]
In Aden, chaos continues to reign in the city where Hadi supporters first drove back the Houthis and allied supporters of former president Ali Abdullah Saleh in July.
On Monday, gunmen on motorcycles shot dead Rasheed Khaled Saif and Hamdi al-Shutairi, two military commanders of the Popular Southern Resistance -- a loose alliance which had helped oust the Houthis with Arab support.
No group immediately claimed responsibility for the killings, which followed the shooting of a senior security official in Aden on Sunday.
Al Qaeda militants have exploited the power vacuum and moved into a major neighborhood of Aden, while unknown assailants blew up the intelligence headquarters in the city.
Residents have complained that police have largely quit the streets and that despite the ejection of the Houthis, Hadi's government has yet to return from Saudi Arabia.
Plans to set up a temporary administration in Aden have been dogged by the disorder.
"We finished the war and the Houthis, but this series of assassinations is really worrying us. There's a security vacuum, the people hope some kind of authority can be established and the police will be deployed so we can be put at ease," said local construction worker Mohammed Ahmed Salem.
The northern-based Houthis seized Sanaa in September 2014 then took control of much of the Arabian Peninsula country. Loyalist forces, supported by Saudi-led air strikes, have made significant advances since July however.
Gulf states regard the Houthis as a proxy of their arch-rival, Shi'ite Iran, while the Houthis say they are fighting a revolution against corrupt officials beholden to the West.
Reporting by Mohammed Mukhashaf in Aden, Mohammed Ghobari in Sanaa and Stephanie Nebehay in Geneva; Writing by Sami Aboudi and Noah Browning; Editing by Mark Heinrich