Legal assistance for the release of Oschadbank collectors

I read the news that Oschadbank collectors, who were transporting money and gold between banks under an international agreement, were detained in Hungary, and their whereabouts are currently unknown. It is said that this could be an illegal seizure or even state terrorism. Please advise what real legal actions the Ukrainian authorities can take to bring our people and valuables home, and are there international protection mechanisms for bank employees in such a situation?