US Secretary of State Antony Blinken has attacked Russian attempts to sow discord in democracies with misinformation after hinting that the Biden administration may soon allow Ukraine to use American-supplied munitions to strike inside Russia.

In Prague for a Nato foreign ministers meeting, Mr Blinken hit out at Moscow’s use of misinformation and disinformation, calling it a “poison”, and signing an agreement with the Czech government to combat it.

He also toured a Czech military base, where he saw armoured vehicles that Prague is sending to Kyiv to help fight Russia’s invasion, and received a briefing on a Czech initiative to supply Ukraine with a million rounds of ammunition by the end of the year.

“We know that a major front in the competition that we have, the adversarial relationship that we have, notably with Russia, is on the information front,” he said.

Mr Blinken said the agreement with the Czechs – the 17th such accord the US has signed with partner nations – will help “to effectively deal with misinformation and disinformation, which is a poison being injected into our democracies by our adversaries”.

“The more we’re able to do together both between our countries but also with other countries, the more effective we’re going to be exposing it and dealing with it,” he told reporters at a signing ceremony with Czech Foreign Minister Jan Lipavsky.

Mr Lipavsky agreed, noting that Czech authorities have recently exposed a major Russian-backed misinformation campaign.

“We are facing confrontation between democracies and autocracies,” he said. “The Kremlin has started targeting democracies all around the world with cyber warfare, propaganda and influence operations, and this danger simply cannot be underestimated any more.”

Russia’s invasion of Ukraine and support for Ukrainian attempts to repel it will be a major focus of the Nato foreign minister meetings on Thursday and Friday – the alliance’s last major diplomatic gathering before a leaders’ summit in Washington in July to mark the 75th anniversary of its founding.

On Wednesday in Moldova, Mr Blinken said US policy on how Ukraine deploys American weapons is constantly evolving, suggesting that Washington may rescind an unwritten prohibition on Ukraine’s use of them for attacks on Russian territory.

Although US officials insist there is no formal ban, they have long made clear that they believe the use of American weapons to attack targets inside Russia could provoke an escalatory response from Moscow, something that Russian President Vladimir Putin has promised.

That position appears to be being reconsidered, and Mr Blinken noted that it is a “hallmark” of the Biden administration’s stance on Ukraine to “adapt and adjust” as needed.

The US Secretary of State visited Kyiv earlier this month and heard a direct appeal from Ukrainian President Volodymyr Zelensky to use American military assistance to strike positions in Russian from where attacks on Ukraine are launched.

“As the conditions have changed, as the battlefield has changed, as what Russia does has changed in terms of how it’s pursuing its aggression, escalation, we’ve adapted and adjusted too, and I’m confident we’ll continue to do that,” Mr Blinken said at a news conference in Chisinau.

“At every step along the way, we’ve adapted and adjusted as necessary, and so that’s exactly what we’ll do going forward,” he said.

“We’re always listening, we’re always learning, and we’re always making determinations about what’s necessary to make sure that Ukraine can effectively continue to defend itself, and we’ll continue to do that.”

Earlier this week, French President Emmanuel Macron and Nato chief Jens Stoltenberg said Western countries should not object if Ukraine needs to strike inside Russia to defend itself.

Mr Stoltenberg reaffirmed that position on Thursday.

“I believe that time has come to (re)consider some of these restrictions to enable the Ukrainians to really defend themselves,” he said.

“We need to remember what it is. This is a war of aggression launched by choice by Moscow against Ukraine.”

The right to self-defence, Mr Stoltenberg said, “includes also striking legitimate military targets outside Ukraine”.