Nato must improve its defensive capabilities and willingness to act in the wake of increasingly aggressive and unpredictable actions by Russia, the head of the transatlantic alliance said in a German newspaper interview published on Sunday.

The Nato secretary general, Jens Stoltenberg, said he expected the German chancellor, Angela Merkel, and other Nato leaders to revamp their approach at the next Nato summit this summer, given a risk that Russia could gradually give more weight to nuclear weapons in its doctrine, exercises and new military capabilities.

“I think Chancellor Merkel and her colleagues will face new decisions at the Nato summit in July in Brussels. We must be alert and resolute,” Stoltenberg was quoted saying by Welt am Sonntag.

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The Nato leader last week accused Russia of trying to destabilise the west with new nuclear weapons, cyber attacks and covert action, including the poisoning of a Russian former double agent and his daughter in the British town of Salisbury.

“We can always do more and must reflect on that now. Salisbury follows, by all appearances, a pattern we’ve observed for some years – Russia is becoming more unpredictable and more aggressive,” he said.

Russia denies any involvement and says it is the US-led transatlantic alliance that is a risk to peace in Europe.

“Russia must not miscalculate,” Stoltenberg told the newspaper. “We are always ready to respond when an ally is attacked militarily. We want credible deterrence. We don’t want any war. Our goal is de-escalation.“

Timeline Poisoned umbrellas and polonium: Russian-linked UK deaths Show Hide Georgi Markov In one of the most chilling episodes of the cold war, the Bulgarian dissident was poisoned with a specially adapted umbrella on Waterloo Bridge. As he waited for a bus, Markov felt a sharp prick in his leg. The opposition activist, who was an irritant to the communist government of Bulgaria, died three days later. A deadly pellet containing ricin was found in his skin. His unknown assassin is thought to have been from the secret services in Bulgaria. Alexander Litvinenko The fatal poisoning of the former FSB officer sparked an international incident. Litvinenko fell ill after drinking tea laced with radioactive polonium. He met his killers in a bar of the Millennium hotel in Mayfair. The pair were Andrei Lugovoi – a former KGB officer turned businessman, who is now a deputy in Russia’s state Duma – and Dmitry Kovtun, a childhood friend of Lugovoi’s from a Soviet military family. Putin denied all involvement and refused to extradite either of the killers. German Gorbuntsov The exiled Russian banker survived an attempt on his life as he got out of a cab in east London. He was shot four times with a silenced pistol. He had been involved in a bitter dispute with two former business partners. Alexander Perepilichnyy The businessman collapsed while running near his home in Surrey. Traces of a chemical that can be found in the poisonous plant gelsemium were later found in his stomach. Before his death, Perepilichnyy was helping a specialist investment firm uncover a $230m Russian money-laundering operation, a pre-inquest hearing was told. Hermitage Capital Management claimed that Perepilichnyy could have been deliberately killed for helping it uncover the scam involving Russian officials. He may have eaten a popular Russian dish containing the herb sorrel on the day of his death, which could have been poisoned. Boris Berezovsky The exiled billionaire was found hanged in an apparent suicide after he had spent more than decade waging a high-profile media battle against his one-time protege Putin. A coroner recorded an open verdict after hearing conflicting expert evidence about the way he died. A pathologist who conducted a postmortem examination on the businessman’s body said he could not rule out murder. Scot Young An associate of Berezovsky whom he helped to launder money, he was found impaled on railings after he fell from a fourth-floor flat in central London. A coroner ruled that there was insufficient evidence of suicide. But Young, who was sent to prison in January 2013 for repeatedly refusing to reveal his finances during a divorce row, told his partner he was going to jump out of the window moments before he was found.

Skripal poisoning Sergei Skripal and his daughter Yulia were were found unconscious on a bench in the Maltings shopping centre in Salisbury after 'suspected exposure to an unknown substance' which was later identified as chemical weapon novichok. In the aftermath Theresa May blamed Vladimir Putin and expelled 23 Russian diplomats who were suspected of spying. Two Russian men using the identities Ruslan Boshirov and Alexander Petrov were named as suspects. They appeared on Russian TV to protest their innocence.

The Skripals survived. However a local woman, Dawn Sturgess, died after spraying novichok on her wrists from a fake Nina Ricci perfume bottle converted into a dispenser, which had been recovered from a skip by her partner Charlie Rowley.

Stoltenberg said hybrid warfare could be added to the agenda of the next Nato-Russia council, a forum that brings together Nato ambassadors and Russia’s top diplomat to the alliance, despite the suspension of joint exercises and peacekeeping operations.

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“Hybrid warfare is a possible topic for the Nato-Russia council. We are now preparing the next meeting, so I don’t want to say too much,” he told the newspaper, referring to increased use of “hybrid tactics” such as soldiers without insignia.

“It’s important that we sit together at the table and speak to each other,” he said, urging Russia to abide by nuclear arms control treaties.

Stoltenberg listed as evidence of Russia’s threat its 2014 annexation of Crimea, support for separatists in Ukraine, military presence in Moldova and Georgia, meddling in western elections and involvement in the war in Syria.