* Army to deploy to major cities after attack * Twenty foreign tourists among dead * Gunmen identified, nine others arrested (Updates with White House statement) By Tarek Amara TUNIS, March 19 (Reuters) - Tunisia said it would deploy the army to major cities and arrested nine people on Thursday after 20 foreign tourists were shot dead in an attack on a museum which Islamic State militants called "the first drop of the rain". Officials did **t confirm the militants' claim of responsibility, but said they had identified two gunmen shot dead by security forces after the shootings, which targeted tourist buses visiting the Bardo museum on Wednesday. Cruise liner MSC Cruises said 12 of its passengers, including Colombians, French and a Belgian, were among the dead, while a Spanish couple was found alive on Thursday after hiding all night in the museum. The assault -- the most deadly attack involving foreigners in Tunisia since a 2002 suicide bombing in Djerba -- came at a fragile moment for a country just emerging to full democracy after its pioneering popular uprising four years ago.