The US has extended a nuclear arms control agreement with Russia for five years, striking the deal despite the Biden administration’s promise to take a harder line on Moscow amid rising tensions between the two countries.

President Joe Biden’s administration defended the decision to extend the treaty before the February 5 deadline without making additional demands, saying it lowered the risks of war and helped prevent arms races.

“Especially during times of tension, verifiable limits on Russia’s intercontinental-range nuclear weapons are vitally important,” Antony Blinken, secretary of state, said in a statement on Wednesday.

The 2011 New Start agreement, which was ratified by the Senate, sets verifiable limits on the numbers of US and Russian intercontinental ballistic missiles, submarine-launched ballistic missiles and heavy bombers.

Mr Blinken said the US remained “clear-eyed” about the challenges posed by Russia to the US and to the world. The White House has promised to work to hold Russia to account for “its reckless and adversarial actions”.

Mr Blinken’s statement comes the day after he called for the “immediate and unconditional release” of Russian opposition activist Alexei Navalny, who was sentenced on Tuesday to three-and-a-half years in prison.

The judge ruled that Mr Navalny, the most prominent critic of Russian president Vladimir Putin, had violated the terms of a suspended sentence for fraud he received in 2014 by not immediately returning to Russia from Germany after recovering from nerve agent poisoning last autumn.

The US is already reeling from a huge cyber-espionage attack on government computers that security officials have blamed on Russia. Mr Biden has asked his intelligence community for its assessment over whether Russia interfered in last year’s elections as well as allegations that Russia promised bounties for the killing of US soldiers in Afghanistan.

The Trump administration was regularly accused of mollifying Moscow, and allegations over suspected ties between Moscow and Donald Trump and his allies cast a pall over his presidency, leading to a two-year investigation into his election campaign.

New Start is the last remaining major defence pact between the former cold war rivals after the Trump administration withdrew from agreements banning intermediate-range nuclear missiles and allowing surveillance flights over each others’ territory.

The Trump administration had also repeatedly tried to strike a more advantageous arms control deal for the US with Russia. It failed to secure a shorter one-year extension, which it sought in order to extract further concessions.

It had also wanted to include China in the agreement, an unlikely prospect that underlined US fears over Beijing’s comparatively small but modern and growing nuclear arsenal.

A report from the Pentagon last year estimated Chinese nuclear warheads numbered in the “low 200s”. The New Start treaty sets the limit for US and Russian nuclear warheads at 1,550.

Mr Blinken has said the Biden administration also wants to pursue arms control with China and a wider agreement with Moscow, adding that the US would use the time provided by the extension to try to strike a wider arms control agreement to address all of Russia’s nuclear weapons.

John Tierney, executive director of the Center for Arms Control and Non-Proliferation, said the Biden administration stood a higher chance of success than the Trump White House.“Trump never established himself or his administration as a serious partner or negotiator while Biden and his team have a reputation for honest engagement, and the ability to execute,” he said, adding that the Trump administration’s demand to include China was “either incompetence or disingenuous — more likely a touch of both”.“The Biden administration showed its intent to prioritise and to identify the importance of treaties’ integrity and the need to deal with other treaty parties genuinely and sincerely.”