Russian President Vladimir Putin on Wednesday ordered top officials to come up with proposals for the potential resumption of nuclear testing for the first time since the end of the Cold War more than three decades ago.

Last week, U.S. President Donald Trump instructed the Pentagon to “immediately” start testing nuclear weapons “on an equal basis” with nuclear testing programs in other nations.

Putin, speaking at Russia’s Security Council, told the country’s foreign and defense ministers, its special services and the relevant civilian agencies to study the matter and “submit coordinated proposals on the possible commencement of work to prepare for nuclear weapons testing.”

Defense Minister Andrei Belousov told Putin at the meeting that it would be “appropriate to immediately begin preparations for full-scale nuclear tests.”

Kremlin spokesperson Dmitry Peskov later clarified that “the president did not give the order to begin preparations for the test” but merely ordered a feasibility study.

Russia announced last week that it had successfully tested a nuclear-powered torpedo, dubbed Poseidon, that was capable of damaging entire coastal regions as well as a new cruise missile named the Burevestnik, prompting Trump to respond. The U.S. today launched an intercontinental ballistic missile, Minuteman III, in a routine test.

The Cold War was characterized by an intense nuclear arms race between the U.S. and the Soviet Union as the superpowers competed for superiority by stockpiling and developing nuclear weapons. It ended in 1991 with the collapse of the Soviet Union and the signing of nuclear treaties such as START, which aimed to reduce and control nuclear arsenals. The Soviet Union conducted its last test in 1990 and the U.S. in 1992.

A report this year by the SIPRI think tank warned that the global stockpile of nuclear weapons is increasing, with all nine nuclear-armed states — the U.S., U.K., Russia, France, China, Pakistan, India, Israel and North Korea — upgrading existing weapons and adding new versions to their stockpiles.