The Pentagon's No. 2 leader says Russia is "playing with fire" by suggesting it would threaten the use of nuclear weapons in territorial disputes.

Robert Work, the deputy secretary of defense, tells a House committee he's worried by what he calls Russian provocations. He describes Moscow's defense strategy as seeking to control the escalation of security tensions by raising the nuclear ante.

Work was testifying Thursday on the administration's approach to modernizing the U.S. nuclear arsenal, which is hampered in some cases by outdated equipment and facilities, at a cost some say is unaffordable given budget constraints and other priorities.

Work said the administration still aspires to a world without nuclear weapons but first must deal with the fact that Russia and China are modernizing their nuclear arsenals.