Russia's top diplomat says that Moscow will observe the limits of the last nuclear arms pact with the United States that expired last week as long as it sees that Washington does the same. The New START treaty expired Feb. 5, leaving no restrictions on the two largest atomic arsenals for the first time in more than a half-century and fueling fears of an unconstrained nuclear arms race. Russian Foreign Minister Sergey Lavrov said Wednesday that even though the U.S. hasn’t responded to President Vladimir Putin’s offer to maintain New START's caps for another year, Moscow will respect the treaty's limits if the U.S. observes them too.