WASHINGTON — US President Joe Biden and his Russian counterpart Vladimir Putin discussed both countries’ willingness to extend the New Strategic Arms Reduction Treaty (New START) for five years, agreeing to have their teams work urgently to complete the extension by Feb 5.

The two leaders also agreed to explore strategic stability discussions on a range of arms control and emerging security issues, the White House said in a statement.

The arms control treaty — signed in 2010 and due to expire on Feb 5, which limits the numbers of deployed strategic nuclear warheads to 1,550 and delivery systems to 700 for each — is the last remaining nuclear arms control pact in force between the two nuclear superpowers.

The treaty can be extended by a maximum of five years with the consent of the two countries. Russia has proposed either an extension to the pact or a new agreement on the limitation of strategic offensive arms, which, the government said, was rejected by the US administration of then president Donald Trump.

On Jan 25, Biden said extending the nuclear arms treaty has to be prioritized.

“I find we can both operate in mutual self-interest of our countries as a New START agreement and make it clear to Russia that we are, we are very concerned about their behavior,” Biden told reporters at the White House.

Russian officials had begun talks with their US counterparts on a possible extension of a key nuclear weapons agreement.

The “practical” work on prolonging the New START has started, said Maria Zakharova, a spokeswoman for the Foreign Ministry.

The secretary of Russia’s Security Council, Nikolai Patrushev, had discussed the issue in a phone call with US National Security Adviser Jake Sullivan, Zakharova confirmed.

The gestures from both sides were welcomed by NATO Secretary-General Jens Stoltenberg.

“We should not end up in a situation where we have no limitation whatsoever on nuclear warheads,” Stoltenberg said.

Kremlin spokesman Dmitry Peskov stressed that “it is of great importance to respect each other’s concerns and take into account Russia’s well-known position on the issue”.

Meanwhile, differences remain on issues of Syria, Ukraine and Iran as well as cybersecurity and mutual accusation of interference in domestic politics. Biden in the phone call reaffirmed US support for Ukraine’s sovereignty.

Biden also spoke with Japanese Prime Minister Yoshihide Suga via phone on Jan 28, their first phone conversation since the American leader was inaugurated.

In talks that lasted about 30 minutes, the two leaders affirmed the importance of the Japan-US alliance and discussed the situation of the Democratic People’s Republic of Korea as well as COVID-19 response and climate change, among other issues, according to Japan’s Foreign Ministry.

Biden invited the Japanese prime minister to take part in a summit on climate change slated for April 22, the ministry said. Suga said he hopes to visit the United States as soon as possible. The issue of holding the Tokyo Olympics and Paralympics, however, was not discussed.

Ren Qi in Moscow contributed to this story.