NAIROBI (Reuters) - One police helicopter and one with military camouflage swooped low over a Kenyan shopping mall on Sunday where security forces were involved in a standoff with Islamist militant gunmen holding hostages, a Reuters witness reported.

Kenyan television reporters said they had been told by officials that they could soon be asked to move further back from the mall.

Minutes earlier, President Uhuru Kenyatta said security forces had "as good a chance to successfully neutralise the terrorists as we can hope for".