The test came as the U.S. prepared sanctions on Russia’s oil and gas sectors and European allies pledged more aid to Ukraine.

Russia will continue to observe the limits set under the recently-expired New START nuclear arms reduction treaty if the United States does the same, Russian Foreign Minister Sergey Lavrov said ...

Russian MP warns US nuclear test plans could destabilize global security, violate CTBT obligations. Follow Newsweek's live blog.

Earlier this month, the New START treaty, a strategic-arms reduction agreement between Russia and the United States to limit their nuclear arsenal, expired. That accord was the last in a series of ...