Russian President Vladimir Putin says his country will explore the possibility of carrying out fresh nuclear tests after US President Donald Trump said last week that Washington would begin nuclear testing programs.

“Russia has always strictly adhered and continues to adhere to its obligations under the Comprehensive Nuclear-Test-Ban Treaty (CTBT), and we have no plans to deviate from these commitments,” Putin said at a meeting with members of Russia’s Security Council Wednesday.

At the same time, however, should the US or other countries who are signatories of the CTBT begin to conduct nuclear weapons tests, “Russia would also have to take appropriate and proportionate responsive measures,” Putin added.

The Russian leader said he had asked government ministries and other agencies to “submit coordinated proposals regarding the possible commencement of work to prepare for nuclear weapons testing.”

Kremlin spokesperson Dmitry Peskov stressed that nothing had been decided yet.

“We are just investigating whether it is necessary to start preparations,” he told CNN. “We are still bound by our obligations on the overall ban of nuclear tests.”

Last week, Putin caused shockwaves when he announced that his country had successfully tested an experimental nuclear-powered underwater torpedo called the Poseidon, which military analysts suggest may have a range of more than 6,000 miles (9,650 kilometers).

Hours later, Trump took to social media to announce that, “because of other countries testing programs, I have instructed the Department of War to start testing our Nuclear Weapons on an equal basis. That process will begin immediately.”

Neither Russia nor the US have tested nuclear weapons since the 1990s, and are both signatories of the CTBT, which bans all nuclear test explosions, no matter their purpose.

Russia’s last nuclear weapons test was in October 1990, after which it pledged to uphold a moratorium on this testing, according to the nonprofit Nuclear Threat Initiative (NTI). The US has not tested a nuclear weapon since 1992, the NTI said.

Russia’s nuclear deterrent must be prepared to face any threat, Belousov said, pointing out that his country’s central test site Novaya Zemlya is ready for any nuclear tests.

Valery Gerasimov, Russia’s chief of the general staff, told Wednesday’s Security Council meeting that the US had “not provided official explanations” regarding Trump’s statement last week, which means that Russia has “no reason to believe that the United States will refrain from preparing for, and subsequently conducting, such tests in the near future.”

“The American side may continue to avoid giving official explanations, but this changes nothing, because if we do not take appropriate measures now, time and opportunities for timely response to US actions will be lost,” he said, noting that the preparation period for nuclear tests can range “from several months to several years.” (CNN)