By Mohammed Ghobari and Mohammed Mukhashaf
SANAA/ADEN (Reuters) - Warplanes from a Saudi-led coalition bombarded Yemen's Houthi-controlled capital Sanaa overnight as the country's warring factions prepared for talks expected to start in Geneva on Monday.
A Reuters witness said the air strikes caused big explosions before dawn and hit locations south and west of Sanaa as part of the coalition's nearly 12-week campaign to target the Houthis and army forces loyal to former President Ali Abdullah Saleh.
On the diplomatic front, United Nations Secretary General Ban Ki-moon was in Geneva for talks aimed at reaching a deal to end the fighting in which more than 2,500 combatants and civilians have been killed since March 19. It was not clear if the opposing factions would meet each other face-to-face.
The U.N. special envoy to Yemen, Ismail Ould Cheikh Ahmed, was expected to meet delegates from both sides separately with the ultimate aim of getting them around the same table.
The exiled Yemeni government's delegation has arrived in Geneva for the talks but a plane carrying representatives of the Houthi's Ansarullah group and Saleh's General People's Congress party was in Djibouti after what Yemeni political sources said was Egypt's refusal to allow plane overflight rights.
There was no immediate comment on the report from Cairo.
"They're stuck, it's a technical glitch, they're in Djibouti," U.N. spokesman Ahmad Fawzi said in Geneva.
It was not immediately clear when the talks, which had already been delayed from Sunday, would start.
Analysts have said there is little sign so far that either the Iranian-allied Houthis and Saleh, or the Riyadh-based President Abd-Rabbu Mansour Hadi are ready to compromise after fighting that has resulted in stalemate since Saudi strikes began on March 26.
While Western countries largely backed Riyadh's air campaign as a way of pushing the Houthis to the negotiating table, they have more recently started to press the kingdom to start a humanitarian pause to allow aid in, and to negotiate.
The crisis began when the Shi'ite Muslim Houthis seized Sanaa last September to little resistance, saying they were trying to root out corruption and discrimination. Hadi fled to Aden in February then escaped to Saudi Arabia as Houthi forces closed in on the southern port city.
Although the conflict is rooted in local rivalries, it has also become part of a wider regional struggle between Sunni Muslim Saudi Arabia and Shi'ite Iran.
It has also forced the United States to withdraw its military personnel from Yemen, seen by Washington as a frontline in its war against Islamist militants.
Fighting raged throughout Yemen's south and center on Monday, in clashes pitting tribesmen and pro-Hadi militiamen against the Houthis and their army allies.
Air strikes hit Houthi positions in Saana on Monday and in the nearby province of al-Dhalea to back up local armed fighters, who exchanged heavy artillery salvos with the Houthis.
Residents in Aden said a Houthi gunmen opened fire on 10 civilians buying ice in a central market on Sunday, killing all of them before being detained by bystanders.
The fighter was released to the militia, whose representatives later apologized to the families of the victims and paid them each 20,000 Yemeni rials ($93 dollars).
It was not possible to independently confirm the reports and much of Yemen remains an inaccessible war zone.
A humanitarian crisis has worsened due to an air and sea blockade imposed to stop arms supplies to the Houthis and Saleh, but which also cut off access to food, medicine and fuel for many citizens.
More than 3,000 cases of dengue fever have been recorded in five provinces since the conflict began, with three confirmed deaths, the World Health Organization said.
Medical sources in Aden say dozens have died from the illness, which has spread from mounting piles of uncollected rubbish and intense summer heat.
(Additional reporting by Tom Miles in Geneva; Writing by Noah Browning and Angus McDowall, editing by Sami Aboudi and Angus MacSwan)