The U.S. decision to allow Ukraine to fire American weapons deeper into Russia has not increased the risk of a nuclear attack, which is unlikely, despite Russian President Vladimir Putin's increasingly bellicose statements, five sources familiar with U.S. intelligence said.

But Russia is likely to expand a campaign of sabotage against European targets to increase pressure on the West over its support for Kyiv, said two senior officials, a lawmaker and two congressional aides briefed on the matter.

A series of intelligence assessments over the past seven months have concluded nuclear escalation was unlikely to result from a decision to loosen restrictions on Ukraine's use of U.S. weapons. That view has not changed following U.S. President Joe Biden's changed U.S. stance this month on weapons, said the sources, who were granted anonymity to speak freely about sensitive intelligence.