Two close aides to Navalny – lawyer Lyubov Sobol and spokeswoman Kira Yarmysh – were among those detained.

Mr Putin focused most of his speech on Russia’s battle against Covid-19 and its plans to improve welfare and economic development.

But he accused the West of threatening stability in Russia and its ex-Soviet neighbours Belarus and Ukraine.

“The use of unjust sanctions is growing into something more dangerous: a coup attempt in Belarus,” he said.

He backs Belarusian President Alexander Lukashenko, who faces huge opposition since claiming re-election last year, in a vote widely condemned as rigged. The two presidents will hold talks in Moscow on Thursday.

On 17 April the Belarusian authorities announced that they had foiled a US-backed plot to assassinate President Lukashenko. Russia’s Federal Security Service (FSB) said it had detained two Belarusians allegedly involved in the plot.

The coup claim was dismissed by the exiled Belarusian opposition leader Svetlana Tikhanovskaya as a “provocation”.

Since last August’s disputed election, massive demonstrations in support of her have taken place, with thousands of protesters beaten up by police and detained.

President Putin said some Western countries were like jackals trying to please the US, just as a jackal behaves with the tiger Shere Khan in Kipling’s tale The Jungle Book.

“We don’t want to burn bridges, but if somebody interprets our good intentions as weakness, our reaction will be asymmetrical, rapid and harsh,” he said. “We’ll decide for ourselves in each case where the red line is.”

Tensions have been building over Ukraine, as reports say Russia has moved more than 100,000 troops close to disputed areas.

A large part of that force is in Crimea, the peninsula which Russia annexed from Ukraine in March 2014. A senior Ukrainian officer, Gen Serhiy Nayev, estimated the total force to be 103,200 last week.

Russia backs the separatists holding a swathe of eastern Ukraine, and its manoeuvres have fuelled fears of a new Russian military intervention.

In his speech Mr Putin said that “the West didn’t think about Belarus or Ukraine, when the Maidan events were going on there”. Mass protests in Kyiv’s Maidan Square led to Ukraine’s pro-Russian President Viktor Yanukovych fleeing to Russia in February 2014.

“The organisers of any provocations against Russia will regret [their actions] in a way they never have before,” Mr Putin warned.

Mr Putin’s spokesman Dmitry Peskov later described the “red lines” as “our external security interests, our internal security interests in preventing any outside interference, whether in our elections or other domestic political processes”.

Last week the US government accused the Kremlin of “malign activity” and expelled 10 Russian diplomats. Russia responded tit-for-tat. Similar hostile exchanges of diplomats took place between Russia and both the Czech Republic and Poland.

The first half of Mr Putin’s speech focused on Russia’s battle with Covid-19 – he praised the social solidarity of millions of people.

Mr Putin, who coughed several times during his speech, said “vaccination is vital… there is no other way”, and he urged all Russians to get vaccinated.

“In the autumn, we want to have achieved collective immunity,” he said. “We must maintain tight control to stop the virus spreading.”

He said Russia was in a demographic emergency, and Covid was making matters worse. The trend must be reversed, to achieve a median life expectancy of 78 years in Russia by 2030, he said.

During the pandemic Mr Putin has largely remained at a residence just outside Moscow, so this is a rare appearance in public.