Here is a summary of these pacts:

- Two multilateral treaties -

In August 1963, the United States, the then Soviet Union, and Britain signed the Nuclear Test-Ban Treaty in Moscow, banning nuclear weapons tests in the atmosphere, in outer space, and underwater.

This was followed by the landmark Treaty on the Non-Proliferation of Nuclear Weapons (NPT), under which nuclear powers agreed not to assist other states in obtaining or producing nuclear weapons.

In force since 1970, the NPT was extended in 1995 for an indefinite period.

- Obsolete bilateral accords -

In May 1972, Moscow and Washington signed SALT I (Strategic Arms Limitation Talks) and the ABM (Antiballistic Missile Treaty).

SALT I froze for five years the number of strategic ballistic missile launchers at existing levels. The ABM, meanwhile, banned the Soviet Union and the US from deploying missile shields.

In June 1979, the powers signed SALT II to set limits on the number of strategic bombers and launchers. But the pact was never applied.

The Intermediate-Range Nuclear Forces Treaty (INF) agreement came into force in May 1988, banning missiles that can travel distances of between 310 and 3,400 miles (500 and 5,500 kilometres).

In August 2019, Washington and Moscow stepped out of the treaty, each accusing the other of violating it.

The two countries said they would develop new missiles and the United States carried out its first intermediate-range missile test since the Cold War.

The Pentagon warned China that the United States now has a free reign to match its military arsenal in Asia.

In July 1991, the two countries agreed to cut their warheads over a period of seven years with the START I treaty, which expired in December 2009.

Another pact, known as START II, was signed in January 1993 after the collapse of the Soviet Union with the aim to further reduce each side's strategic arsenal. But it never came into force.

When the US in 2002 withdrew from the ABM Treaty, Russia withdrew from START II.

The same year, the Strategic Offensive Reductions Treaty (SORT), commonly known as the Moscow Treaty, was signed to cap the number of nuclear warheads.

- One bilateral treaty in force -

SORT was replaced in April 2010 by the new START treaty, which allowed Russia and the US a maximum of 1,550 deployed warheads -- about 30 percent lower than the limit imposed under the 2002 pact. It came into force in February 2011 for 10 years and can be renewed for a maximum of five.

The accord, which also includes reciprocal checks, is up for renewal in 2021.

Negotiations on the treaty resume in Vienna on Monday. Moscow has been demanding negotiations on its renewal since late 2019, but the administration of Donald Trump has dragged its feet, insisting on Beijing's inclusion in the talks.