By Phil Stewart and Idrees Ali
WASHINGTON (Reuters) - The United States believes that Russia fired a never-before-fielded intermediate-range ballistic missile on Thursday in its attack on Ukraine, an escalation that analysts say could have implications for European missile defense.
The U.S. military said the Russian missile's design was based on the design of Russia's longer-range RS-26 Rubezh intercontinental ballistic missile (ICBM). The new missile was experimental and Russia likely possessed only a handful of them, officials said.
Ukraine's air force initially said the missile was an ICBM, sparking worries of a major escalation in the 2-1/2-year-old war.
While launching an intermediate-range ballistic missile (IRBM) sends a less threatening signal, the incident could still set off alarms and Moscow notified Washington briefly ahead of the launch, U.S. officials said.
The Pentagon said the missile was fired with a conventional warhead but added that Moscow could modify it if it wanted.
"It could be refitted to certainly carry different types of conventional or nuclear warheads," said Pentagon spokesperson Sabrina Singh.
Russian President Vladimir Putin, in a televised address, acknowledged Moscow had struck a Ukrainian military facility with a new ballistic missile and said it was called "Oreshnik" (the hazel).
Jeffrey Lewis (JO:LEWJ), a non-proliferation expert at the Middlebury Institute of International Studies in California, said Putin had earlier hinted that Russia would complete the development of an IRBM system after Washington and Berlin agreed to deploy long-range U.S. missiles in Germany from 2026.
"The RS-26 was always (a) prime candidate," Lewis said.
Singh said the new variant of the missile was considered "experimental" by the Pentagon.
"It's the first time that we've seen it employed on the battlefield ... So that's why we consider it experimental," she said.
Timothy Wright, at the International Institute for Strategic Studies, said Russia's development of new missiles may influence decisions in NATO countries regarding what air defense systems to purchase as well as which offensive capabilities to pursue.
A new U.S. ballistic missile defense base in northern Poland has already drawn angry reactions from Moscow. The U.S. base at Redzikowo is part of a broader NATO missile shield and is designed to intercept short- to intermediate-range ballistic missiles. Still, Putin said Thursday's launch of the new IRBM was not a response to the base in Poland but instead to recent Ukrainian long-range strikes inside Russian territory with Western weapons.
After approval from the administration of President Joe Biden, Ukraine struck Russia with U.S.-made ATACMS on Nov. 19 and with British Storm Shadow missiles and U.S.-made HIMARS on Nov. 21, Putin said.
Moscow said it targeted a missile and defense firm in the Ukrainian city of Dnipro, where missile and space rocket company Pivdenmash, known as Yuzhmash by Russians, is based.
Russia, he added, was developing short and medium range missiles in response to the planned production and then deployment by the United States of medium and shorter range missiles in Europe and Asia.
"I believe that the United States made a mistake by unilaterally destroying the treaty on the elimination of intermediate-range and shorter-range missiles in 2019 under a far-fetched pretext," Putin said, referring to the Intermediate-Range Nuclear Forces (INF) Treaty.
The United States formally withdrew from the 1987 (INF) Treaty with Russia in 2019 after saying that Moscow was violating the accord, an accusation the Kremlin denied.