| BOGORODSKOYE, Russia
BOGORODSKOYE, Russia A top Russian diplomat said on Wednesday that talks with the United States on missile defense had hit a "dead end," and Foreign Minister Sergei Lavrov responded coolly to a gesture designed to allay the Kremlin's concerns about U.S. plans.
The remarks by Lavrov and Moscow's NATO envoy, Dmitry Rogozin, underscored the uphill battle the U.S. administration faces in convincing the Kremlin to drop its complaints about an anti-missile system Washington says poses no threat to Russia.
Moscow says the system is a potential threat and is demanding binding guarantees that it would not blunt the deterrent effect of Russia's nuclear arsenal. Talks aimed at turning confrontation into cooperation have brought no deal.
"Negotiations with the United States on missile defense have run into a complete dead end," state-run news agency RIA quoted Rogozin as saying. "We will continue negotiations -- there is still time, but very little."
Both sides earlier said they hoped an agreement could be reached in time for a NATO summit in the United States in May.
Persistent tension over the plan has undermined efforts to build on recent improvements in ties between the former Cold War foes. It is deepened by Russia's uncertainty about future U.S. policy after the November 2012 presidential election.
The United States says the planned shield is not intended to counter Russia's huge arsenal, but is needed to protect against missiles that could be fired by countries with smaller arsenals such as Iran.
Moscow says the system, due to be fully deployed by 2020 with interceptor missiles and radars at sea and in several European countries, would weaken Russia if it can shoot down the nuclear missiles Moscow relies upon as a deterrent.
Stepping up efforts to change Moscow's mind, a Pentagon official said on Tuesday the United States had invited Russia to use its own radars and other sensors to monitor one or more U.S. missile interceptor flight tests.
Lavrov made clear the offer fell far short of Moscow's calls for a role in planning a missile shield and binding guarantees that the system would not weaken Russia.
"We are being invited to monitor the realization of a plan that we see as creating a risk to our forces of deterrence," Lavrov told reporters when asked about the invitation.
Lavrov repeated Russia's complaint that the United States was pushing ahead with its own plans instead of giving Moscow a say in how a European missile shield should look.
"It would be better to ... first collectively create a missile defense architecture that would be guaranteed to be directed outside Europe and would not create threats for anyone inside Europe -- and only then to start putting this system in place and inviting one another to monitor," he said.
The chief U.S. negotiator on missile defense, Undersecretary of State Ellen Tauscher, said on Tuesday the United States was prepared to offer written assurances that the system being built was not directed against Russia, but was not prepared to provide legally binding commitments.
Russia's Interfax news agency cited an unnamed Foreign Ministry official as saying on Wednesday that only legally binding guarantees would suffice.
(Reporting By Gleb Stolyarov; Writing by Alexei Anishchuk; Editing by Steve Gutterman and Peter Graff)