* Four Ugandan helicopters were on way to Somalia
* Three gunships disappeared on Sunday near Mount Kenya
* African forces plan assault on Somali rebels in Kismayu (Adds details, changes dateline)
By Elias Biryabarema
KAMPALA, Aug 13 (Reuters) - Uganda said on Monday the pilot and four crew of a Somalia-bound Ugandan attack helicopter that made an emergency landing in Kenya had been rescued but two other gunships and ten crew members were still missing in the same area.
Ugandan troops form the backbone of the African Union (AU)force (AMISOM) fighting Islamist militants in Somalia. The air force said on Aug. 7 that it was deploying transport and combat helicopters to Somalia to add muscle to the force.
The AU force, which includes Kenyan, Burundian and a handful of Djiboutian troops, is planning an offensive on Somalia's southern port city of Kismayu, a hub for the al Qaeda-aligned al Shabaab rebels.
Poor weather early on Monday hampered a search and rescue operation for the three Russian-built Mi-24 helicopter gunships that went down in the Mount Kenya region on Sunday while en route to reinforcing AU forces in Somalia.
Felix Kulayigye, a spokesman for the Uganda People's Defence Forces (UPDF), said one pilot managed to send out a distress signal after making an emergency landing.
"The one who made an emergency landing has been traced. The pilot and crew have all been rescued. They are all safe," Kulayigye told reporters in the Ugandan capital, Kampala.
"We're yet to confirm the whereabouts of the other two (helicopters) with ten people on board. We have unconfirmed reports they made a hard landing."
Kulayigye said there has been no radio contact with the other two military aircraft since they went missing.
Kenyan and Ugandan officials have not spelled out whether the helicopters were forced down by stormy weather or suffered mechanical failure.
A fourth chopper, an Mi-17 troop carrier, landed on schedule in the eastern Kenyan town of Garissa, a major base for Kenya's military operations inside neighbouring Somalia.
Earlier, Kenya's Department of Defence spokesman Bogita Ongeri said the rescue mission would be intenfified once the bad weather cleared.
Al Shabaab struck the Ugandan capital Kampala in mid-2010 when suicide bombers killed more than 70 people who were watching the World Cup soccer final on television. The attack was in revenge for the presence of Ugandan troops in Somalia. (Additional reporting by Drazen Jorgic in Nairobi; Editing by Richard Lough)