Jan 31, 2014
Russia accused by the US of breaching INF treaty that bans medium-range nuclear missiles tests.
Such a test would fall under the treaty's parameters.
The US has not publicly stated that Moscow is in breach of the treaty but it has now briefed its Nato allies on the issue.
Washington is also reported to have raised concerns with the Russians several times during the past year but has been told that there is no issue to be resolved.
The 1987 INF Treaty was one of the key arms control agreements of the Cold War years.
It eliminated an entire category of nuclear-armed weapons; land-based cruise and ballistic missiles with ranges of between 500km and 5,500km (310 miles and 3,400 miles).
This encompassed US Pershing and Cruise missiles based in Europe, along with the then Soviet Union's SS-20 systems.
Today Russia's missile inventory is complex, often with versions of land, sea and air-launched missiles that bear strong family resemblances.
Experts believe that the cruise missile in question is the R-500; derived from the land-based Iskander-K.
The Russians are no great fans of the INF agreement which they believe - some 26 years after it was signed - reflected a very different world.
It only eliminated these weapons from the US and Soviet/Russian arsenals and, since then, several countries have developed missiles within this range.