Russian President Dmitry Medvedev lashed out Wednesday at the United States over its plans for a missile shield in Europe, saying a U.S. deal to install part of the system in Czech Republic “deeply distresses” Moscow.

He vowed a response to the planned U.S. system but stopped short of specifying what kind.

A day earlier, the Russian Foreign Ministry threatened a military response if the agreement U.S. Secretary of State Condoleezza Rice signed in the Czech Republic is ratified.

Medvedev echoed his predecessor Vladimir Putin’s bitter tone on a topic at the center of strained ties with Washington. He suggested the U.S., instead of honestly addressing Russia’s concerns, has been stringing it along with “halfhearted negotiations that have come to nothing.”

The United States wants to place tracking radar in the Czech Republic and missile interceptors in Poland _ two NATO nations formerly in the Soviet-controlled Warsaw Pact.

“The situation deeply distresses us,” Medvedev said.

“We of course will not raise hysteria over this, but we will think of further steps in response to it,” he said.

Russia says it is not convinced by U.S. insistence that the shield is meant to neutralize a potential Iranian threat and suspects the true aim is to weaken Russia’s nuclear deterrent, altering the balance of power between the Cold War foes.

“We have repeatedly underscored _ both earlier and during this summit I spoke of this _ that questions of European security must be resolved in a different way,” Medvedev told a news conference after a summit of the Group of Eight leading industrialized nations in Japan.

Discord on the missile shield shadowed Medvedev’s talks Monday with President Bush on the sidelines of the summit. While Medvedev stressed Tuesday that Russia wants close, constructive ties with the United States, he said there was no progress on disputes including the missile defense plans.

Shortly after the U.S.-Czech treaty was signed, Russia’s Foreign Ministry said Moscow would be forced to initiate a military response if the deal goes ahead.

If the agreement is ratified, “we will be forced to react not with diplomatic, but with military-technical methods,” the Foreign Ministry statement said. It did not give specifics of what the response would entail.

In February, then-President Putin said that if the plan advances, Russia could aim missiles toward prospective missile defense sites and deploy missiles in its westernmost region, Kaliningrad, which borders Poland.

Russia hopes the next U.S. administration will scrap the plans.