Russian missile test violated landmark treaty, says US Soviet President Mikhail Gorbachev and US President Ronald Reagan at the White House in 1987, the year they signed the landmark arms control treaty. Washington: The United States informed its NATO allies this month that Russia had tested a new ground-launched cruise missile, raising concerns about Moscow's compliance with a landmark arms control accord. US officials believe that Russia began conducting flight tests of the missile as early as 2008. Such tests are prohibited by the treaty banning medium-range missiles that was signed in 1987 by US president Ronald Reagan and Mikhail Gorbachev, the Soviet leader at the time. The treaty has long been viewed as one of the bedrock accords that brought an end to the Cold War. Since May, the State Department's senior arms control official, Rose Gottemoeller, has repeatedly raised the missile tests with Russian officials, who said they investigated the matter and consider the case to be closed. But Obama administration officials are not yet ready to formally declare the tests of the missile, which has not been deployed, to be a violation of the 1987 treaty. With President Barack Obama pledging to seek deeper cuts in nuclear arms, the State Department has been trying to find a way to resolve the compliance issue, preserve the treaty and keep the door open to future arms control accords. "The United States never hesitates to raise treaty compliance concerns with Russia, and this issue is no exception," said State Department spokeswoman Jen Psaki. There's an ongoing review process, and we wouldn't want to speculate or prejudge the outcome. Other officials, who asked not to be identified, said there was no question that the missile tests ran counter to the treaty and that the administration had already shown considerable patience with the Russians. Some members of Congress, who have been briefed on the tests on a classified basis for more than a year, have been pressing the White House for a firmer response. A public dispute over the tests could prove to be a major new irritant in the already difficult relationship between the US and Russia. In recent months, that relationship has been strained by differences over how to end the fighting in Syria, the temporary asylum granted to former National Security Agency contractor Edward Snowden and, most recently, the turmoil in Ukraine. Since President Vladimir Putin rose to power and the Russian military began to re-evaluate its strategy, the Kremlin has developed second thoughts about the treaty. During the administration of George W. Bush, Russian defence minister Sergei Ivanov proposed the two sides drop the treaty. However, since Mr Obama has been in office, the Russians have insisted that they want to keep the treaty, which bans the testing, production and development of medium-range missiles. But in the view of US analysts, Russia has also mounted a determined effort to build up its nuclear abilities to compensate for the weakness of its conventional, non-nuclear forces. It took years for US intelligence to gather information on Russia's new missile system, but by the end of 2011, officials say it was clear that there was a compliance concern. Ms Gottemoeller has said the Obama administration had not given up on diplomacy. There are precedents for working out disputes over arms control complaints, and Ms Gottemoeller said she would continue to engage the Russians to try to resolve the controversy. But even with the best of intentions, establishing what the Russians are doing might not be easy; the elaborate network of verification provisions that were created under the medium-range missile treaty is no longer in effect, since all the systems that were believed to be covered by the agreement were long thought to have been destroyed.