美国：俄罗斯违反1987核导弹条约
Russia has violated a key arms control treaty by testing a nuclear cruise missile, the US government says.
美国政府称，俄罗斯测试一枚核巡航导弹的行为违反了一项关键的军备控制条约。
The agreement was signed towards the end of the Cold War by Mikhail Gorbachev (left) and Ronald Reagan
Russia tested a ground-launched cruise missile, breaking the Intermediate-Range Nuclear Forces Treaty signed in 1987 during the Cold War, the US said.
A senior US official did not provide further details on the alleged breach, but described it as "very serious".
The bilateral agreement banned medium-range missiles with ranges between 500 and 5,500 km.
The US claims come at a time of heightened tensions between the two sides, with the US criticising Russia for its alleged involvement in the conflict in Ukraine.
'Prohibited items'
A senior US official, who was not named, said in a statement that the testing of the missile was "a very serious matter which we have attempted to address with Russia for some time now".
"We encourage Russia to return to compliance with its obligations under the treaty and to eliminate any prohibited items in a verifiable matter," the official added.
US President Barack Obama has written to Russian leader Vladimir Putin over the matter, officials say.
This is the first time the US government has made its accusations public, though the issue has simmered for years, the BBC's Paul Blake in Washington reports.
In January, the New York Times reported that US officials believed Russia had began testing ground-launched cruise missiles as early as 2008.
The US State Department had said at the time that the issue was under review.
The 1987 treaty is at the heart of American-Russian arms control efforts, and was signed by then-Presidents Ronald Reagan and Mikhail Gorbachev in the final years of the Cold War, our correspondent says.