President Obama has informed Russian President Vladimir Putin that the Russians have violated a 1987 arms control treaty. The news was delivered via letter on Monday. The Obama administration found Russia violated this treaty when testing a ground launched cruise missile, according to The New York Times:

It is the most serious allegation of an arms control treaty violation that the Obama administration has leveled against Russia and adds another dispute to a relationship already burdened by tensions over the Kremlin’s support for separatists in Ukraine and its decision to grant asylum to Edward J. Snowden, the former National Security Agency contractor."

The Intermediate-range Nuclear Forces Treaty (INF) dates back to 1987 and prohibits the U.S. and Russia from owning or testing ground launched ballistic and cruise missiles which can fly 300 to 3,400 miles. It was signed by President Reagan and USSR leader Mikhail Gorbachev as they aimed to bring an end to the Cold War. However, in 2008, American intelligence services discovered Russia was testing cruise missiles and Russian officials were notified of the concern in 2013.  The U.S. also discussed Russia's testing of the cruise missile with NATO allies earlier this year. 

Though the U.S. has been aware of the situation for some time, it was first discussed at length by senior intelligence and security officials because the Obama Administration decided to pursue sending the letter.

The New York Times has learned this treaty violation will also be noted in the annual report on international arms control compliance put out by the State Department. It will read:

The United States has determined that the Russian Federation is in violation of its obligations under the I.N.F. treaty not to possess, produce or flight test a ground-launched cruise missile (GLCM) with a range capability of 500 kilometers to 5,500 kilometers or to possess or produce launchers of such missiles."

The U.S. will now seek a resolution to the violation. However, because Russia was notified in 2013 about the general concern, they believe they have done their due diligence in reviewing the issue and that it has been resolved