This was stated in a US State Department statement.
"Russia’s noncompliance with the New START Treaty, and its claimed suspension of the treaty, are unfortunate and irresponsible steps and are also legally invalid. As a result, Russia remains bound by its obligations under the treaty. The United States remains ready to work constructively," the State Department said.
The department noted that Russia’s noncompliance is clear: Russia is refusing to allow inspections in every way possible, which gives the possibility to monitor global nuclear stability. In addition, the Russian side refuses to meet with U.S. experts and give information on the status of its nuclear forces.
Such steps could threaten not only the viability of the Treaty itself, but also global security, according to the United States. In addition, Russia's accusations of non-compliance by the United States "are an attempt to distract attention from Russia's own actions."
It is noted that Russian inspectors have the necessary visas, Russian treaty-designated airplanes have viable air routes to transport inspectors to the U.S., inspectors can also use commercial air travel to reach United States territory, and there are no sanctions that prevent Russia from fully exercising its inspection rights.
"We remain ready for constructive engagement today - this is an important element of nuclear stability. There are no legal grounds for suspending the treaty," the US said.
For reference. The Strategic Arms Reduction Treaty (START) is an agreement between the United States and Russia on mutual reductions and limitations of nuclear weapons.
On February 28, Russian President Vladimir Putin signed a decree to temporarily suspend Russia's participation in the Strategic Arms Reduction Treaty.