"I reassured President Trump that Russia stands ready to extend this treaty, to prolong it, but we have to agree on the specifics at first, because we have some questions to our American partners," Putin told Fox News in an interview after a summit with Trump on Monday in Helsinki.
"We think that they are not fully compliant with the treaty, but this is for experts to decide," Putin added.
The New START treaty, signed on April 8, 2010, calls for deployable nuclear warheads and bombs to be capped at no more than 1,550. It limits deployed intercontinental ballistic missiles, submarine-launched ballistic missiles and nuclear bombers to 700 and non-deployed ICBMs, SLBM and bombers to 800.
The treaty lasts for 10 years and can be extended by up to five years. The New START treaty gave both countries until February this year to reach the treaty limits.
Both sides say they met the treaty caps earlier this year, but Russia has raised questions about the U.S. conversion of some submarines and bombers to carry conventional weapons, saying it has no way to verify they cannot also be used for nuclear arms.
While Trump has criticized the treaty as a bad deal negotiated by his predecessor, proponents of the accord say it is important because it created a new monitoring regime, including data exchanges, that enable the two sides to verify compliance.