UPDATE 10-Islamist gunmen hold hostages in Kenya siege, 68 dead
* Somali Islamists linked to al Qaeda claim attack
* Group wants withdrawal of Kenyan troops from Somalia
* President loses relatives in raid, vows punishment
* Volleys of gunfire, helicopters swoop low over mall
By Richard Lough and Edmund Blair
NAIROBI, Sept 22 (Reuters) - Islamist militants were holding hostages on Sunday at a shopping mall in Nairobi, where at least 68 people were killed in an attack by Somalia's al Shabaab group.
The al Qaeda-affiliated movement demanded Kenya pull troops out of its northern neighbour, where they have pushed al Shabaab onto the defensive over the past two years.
There was no word of other demands from the dozen or so gunmen - and possibly women - said to be barricaded in a supermarket with an unknown number of captives. One Kenyan TV station said 30 were still being held, nearly 36 hours after Saturday's devastating assault.
Brief volleys of gunfire and a blast interrupted a day of stalemate. A Reuters correspondent saw security personnel on the move and, as dusk closed in, two helicopters swooped low over the Westgate shopping centre, which has several Israeli-owned outlets and is frequented by prosperous Kenyans and foreigners. Continued...