UPDATE 1-Less than 30 Britons at risk in Algeria -UK's Cameron

LONDON, Jan 18 (Reuters) - British Prime Minister David Cameron said on Friday he was disappointed Algeria had not informed him in advance of its operation to rescue hostages being held in a desert gas facility and said less then 30 Britons were still "at risk".

Promising that the hostage takers would be hunted down, he told parliament the situation was still dangerous and that the Islamist captors still posed a threat in one part of the site despite an assault by Algerian forces the previous day.

At least 18 foreign hostages were unaccounted for on Friday and their al-Qaeda-linked captors threatened to attack other energy installations after Algerian forces stormed the gas complex to free hundreds of captives, resulting in dozens of deaths.

While contacts with the Algerian authorities had been "good", Cameron said he was "disappointed not to be informed of the assault in advance and we do want to help in any way we can with technical help and assistance". He said the Algerians had made no request for assistance.

The situation was unfolding on sovereign Algerian territory and the authorities there had the right to handle things as they saw fit, he said, however, adding he understood the decision to act had been taken because of an "imminent" threat to lives.

He said the number of Britons being held was now "significantly" less than 30. Some reports have put the number at between ten and 20.