Jailed Russian government critic Alexei Navalny has told supporters that "everything is fine" in a first message from a detention centre outside Moscow.
In the message posted on Instagram, President Vladimir Putin's most prominent detractor said he was being held in the Kolchugino detention centre in the Vladimir region northeast of Moscow.
"But everything is fine with me, there's even a chin-up bar in the exercise yard here," he said.
Mr Navalny was jailed last month when he returned from Germany where he was recovering from exposure to a nerve agent.
He was sent to a penal colony for two and a half years for allegedly violating the terms of a suspended sentence.
Meanwhile, Russia has hit back at Western countries for sanctioning senior Russian officials over the poisoning of Mr Navalny, warning its enemies "not to play with fire".
The Kremlin accused Washington and Brussels of interference after the United States and the European Union introduced fresh penalties yesterday.
The sanctions further erode ties between Moscow and the West since Russia's annexation of Crimea in 2014.
"We believe such measures are absolutely unacceptable because they significantly damage already bad relations" with Washington and Brussels, Kremlin spokesman Dmitry Peskov told reporters.
He said the new sanctions amounted to "interference" in Russia's domestic affairs and vowed to take action in response, without specifying measures.
Mr Peskov's comments echoed foreign ministry spokesperson Maria Zakharova who warned the West earlier "not to play with fire" and said Russia would respond according to "the principle of reciprocity".
"We will continue to systematically and resolutely defend our national interests and rebuff aggression," she said in a statement.
Ms Zakharova later said Russia was already formulating its response, without giving details.
The sanctions announced by Washington signal a harder line from US President Joe Biden and target several individuals within Russia's security sector, including Federal Security Service (FSB) head Alexander Bortnikov.
But Mr Peskov again denied Russian involvement in the poisoning of Mr Navalny and said that claims the FSB was involved in a poisoning attack were "outrageous".
He maintains that his near fatal attack was carried out by the FSB on the orders of President Putin, a claim vehemently denied by the Kremlin.
Mr Navalny was flown to Germany in August for treatment after falling violently ill on a flight from Siberia. European laboratories later concluded he was poisoned with the Soviet-era nerve agent Novichok.
He returned to Moscow in January only to be arrested and then sent to a penal colony for two-and-a-half years for allegedly violating the terms of a suspended sentence.
Mr Navalny's return and imprisonment sparked mass nationwide rallies in late January.
Both Washington and Brussels have demanded his immediate release while two United Nations human rights experts called for an international investigation into his poisoning.