Malaysian Airlines officials have confirmed that nine Britons were on board the passenger aircraft which was shot down over Ukraine yesterday.
Around 100 of those on board the flight were delegates heading to a conference on AIDS in Melbourne, Australia.
It is not clear if any of the Britons were from Northern Ireland, but it has been confirmed that one was Glen Thomas, a 49-year-old media relations officer who had previously worked in the BBC.
Malaysia Airlines have released figures saying flight MH17 was carrying at least 173 Dutch nationals, 44 Malaysians (including 15 crew), 27 Australians,12 Indonesians and nine Britons.
British Foreign Secretary Philip Hammond said: "We're determined to get to the bottom of understanding what has happened here.
"As yet, we do not have any definitive information about how this incident occurred and I don't want to speculate at this stage. We believe that there must be a UN-led international investigation of the facts."