Russia's Putin warns nuclear arms control system risks breaking down

ST PETERSBURG (Reuters) - Russian President Vladimir Putin warned on Thursday there was a significant risk that the international system for nuclear arms control could break down, saying talks with Washington on extending the New START nuclear arms treaty had yet to begin.

Speaking in televised comments from St Petersburg, Putin said his most recent phone conversation with U.S. Donald Trump had, however, give him some cause for optimism.

(Reporting by Vladimir Soldatkin, Maria Kiselyova; writing by Tom Balmforth; editing by Andrew Osborn)