Navalny was arrested in January upon returning from Germany after recovering from a nerve agent poisoning attack he says was orchestrated by the Kremlin.
Navalny barely survived a poisoning with the Novichok nerve agent in August which he has blamed on the Kremlin. His doctors say his hunger strike might have exacerbated his condition.
Navalny, 44, a prominent opponent of Russian President Vladimir Putin, started refusing food on March 31 in protest at what he said was the refusal of prison authorities to treat him properly for acute back and leg pain.
"His condition is indeed critical," said Alexandra Zakharova, a representative of the Doctors Alliance trade union - a group that Russian authorities regard as opposition activists.
"The hostility and unpredictability of America's actions force us in general to be prepared for the worst scenarios," Kremlin spokesman Dmitry Peskov told reporters.
Moscow's ties with Washington nosedived last month when Russia recalled its ambassador after US President Joe Biden said he thought President Vladimir Putin was a killer.
Navalny, one of President Vladimir Putin's most prominent critics, has separately complained of acute back and leg pain and accused authorities of refusing him access to his chosen doctor and of declining to supply him with the right medicine.
Russia has since March impeded the speed of Twitter for not removing content it deems illegal, and threatened to block it entirely. Photos and videos take longer to load for some users.
"It was a productive discussion about how we can both work to ensure that reports of such illegal content are dealt with expeditiously," it said in a statement.
The Tagansky District Court in Moscow said in a series of statements that it had issued three separate fines against Google of 3.2 million roubles, 3.3 million roubles and 2.4 million roubles.
It said the fines related to offences committed on Jan. 22-24 this year, including "violating the procedure for removing information", all under Russia's Administrative Offences Code.
OVD-Info, which monitors the detention of political protesters and activists, published a list of more than 150 people it said had been detained.
"The police came to the forum of municipal deputies in Moscow. There are 150 people here from all over the country. Everyone is being detained. I mean, everyone," opposition politician Ilya Yashin wrote on Twitter.
Rouble was 0.7% stronger against the dollar at 73.64 and had gained 0.8% in volatile trade to 88.60 versus the euro.
A trader at an investment company in Moscow told Reuters that reports of softer sanctions expected to be imposed by the United States were largely behind the rouble's swing.
Around 120 km is left to be laid in Danish waters as well as almost 30 km in German waters, before it makes landfall at the northern German coastal town of Lubmin, near Greifswald.
The project has become more politicised after Kremlin critic Alexei Navalny, who was poisoned in August in Siberia and flown to Germany for treatment.
"I stand in solidarity with the three countries that have had their diplomats expelled," Macron told a news conference following a virtual meeting of the France-German Defence and Security Council.
Russia on Friday announced the expulsion of diplomats from Sweden, Germany and Poland, accusing them of taking part in illegal protests last month against the jailing of Kremlin critic Alexei Navalny.
I made it clear to President Putin, in a manner very different from my predecessor, that the days of the United States rolling over in the face of Russia's aggressive actions.
"This is very aggressive, unconstructive rhetoric, to our regret," said Peskov.