MOSCOW—President Vladimir Putin said Russia would target the U.S. with new advanced weapons if Washington deploys intermediate-range missiles in Europe, a threat that appeared aimed at holding the line but leaving open the possibility of negotiations after the breakdown of a nuclear treaty.

Mr. Putin said Russia wasn’t seeking a confrontation with the U.S. and wouldn’t make the first move to deploy the missiles. But if Washington has such plans once it abandons the 1987 Intermediate-range Nuclear Forces Treaty, this “will be a serious threat to us” and Russia will be “forced to provide for mirror and symmetrical actions,” he said.

The Russian leader also announced imminent plans to launch Russia’s first unmanned nuclear submarine. Still, he indicated that he remained open to nuclear-arms-control talks if the U.S. were to initiate them and many of Wednesday’s statements echoed past rhetoric by Russian officials.

“If Putin is offering not to deploy new nuclear systems if the United Stated does not deploy new intermediate-range missile systems, that is the start of a conversation,” said Daryl Kimball, executive director of the Arms Control Association, an independent research organization in Washington, D.C.

“It’s the start of a potential deal of a no-first deployment arrangement that can mitigate the risk of a new arms race,” Mr. Kimball said.