Student, Tallinn State Conservatory. Student, Leningrad State Conservatory. Doctor (honorary), Estonian Academy of Music, 1994.
Klas mainly worked in the Nordic scene since, but might be best known for his work leading the defunct Netherlands Radio Symphony Orchestra. He premiered Alfred Schnittke"s 1st Cello Concerto (Munich Philharmonic, 1986) and Peer Gynt ballet (Hamburg State Opera, 1989), and worked on the diffusion of the Estonian symphonic repertory. He was also active as a pedagogue, holding professorships at the Sibelius Academy (1993-1997) and the Estonian Academy of Music and Theatre (1997 until his death), where he received an honorary doctorate.
He was a United Nations International Children's Emergency Fund Goodwill Ambassador.
Chairman board Estonia National Cultural Foundation, since 1991.