China dismissed on Tuesday the United States' claims that it was dramatically expanding its nuclear capabilities, saying that was untrue.

Fu Cong, director-general of the Foreign Ministry's Department of Arms Control, said at a news briefing that China has adopted a no-first-use nuclear policy and maintained its nuclear capabilities at the minimum level required for national defense.

"We do not deny that China has taken measures to modernize our nuclear arsenal, not for other reasons, but for reliability and safety reasons," he said.

It is the US that should be blamed, Fu said, as some of its actions changed the security dynamics. These included withdrawal from international agreements, in particular in the area of arms control, as well as spending trillions of dollars to upgrade its nuclear arsenal.

In response to the US moves, China needed to assess the sufficiency of nuclear forces according to the changing security environment, and take measures to make sure its nuclear deterrent forces were viable and capable of performing their assigned tasks, he said.

The news briefing was held after the five nuclear weapon states－China, France, Russia, the United Kingdom and the United States, which are also permanent members of the United Nations Security Council－for the first time issued a joint statement on nuclear weapons on Monday, aiming at preventing nuclear war and avoiding an arms race.

The statement was issued after the Tenth Review Conference of the Parties to the Treaty on the Non-Proliferation of Nuclear Weapons was postponed from Tuesday to later in the year due to the COVID-19 pandemic.

As an initiator of the joint statement and a contributor to its content, China has made a great contribution to the statement, Fu said, adding that the statement reflected the largest convergence yet of the five nuclear weapon states' nuclear policies.

Noting that the US and Russia still possessed over 90 percent of all existing nuclear weapons, Fu said that if the two nuclear powers continued to reduce nuclear stockpiles to China's level, China would be happy to join the two countries for nuclear negotiations. China does not shy away from its obligations and has shown great restraint in its development of nuclear weapons, he added.

"They must reduce their nuclear arsenal in an irreversible and legally binding manner," Fu said.