BERLIN — Aleksei A. Navalny, the Russian opposition leader who is recovering in Berlin after being poisoned, posted a photograph on Tuesday showing him in the hospital, looking gaunt but very much alive, and telling followers that he was breathing on his own.
“Hello, it’s Navalny,” he said in an Instagram post with a picture of himself sitting up in a hospital bed surrounded by his wife and other relatives. “I can still do almost nothing, but yesterday I could breathe the entire day by myself.”
The message came hours after a senior German security official told The New York Times that Mr. Navalny was awake, alert and had told German prosecutors that he was refusing to cooperate with a Russian inquiry into his case. He also vowed, according to the official, to return to Russia as soon as possible to continue his work.
Mr. Navalny’s spokeswoman, Kira Yarmysh, confirmed on Tuesday that Mr. Navalny planned to return to Russia.
“It’s strange to me that anyone could think otherwise,” Ms. Yarmysh said on Twitter. “No other options are being considered.”
Asked whether Mr. Navalny would be permitted to return to Russia, the Kremlin’s spokesman, Dmitri Peskov, said that “any Russian citizen” was allowed to leave and enter the country at will.
Mr. Navalny’s return to health, as well as to social media, has the potential to re-energize Russia’s opposition after nearly a month of uncertainty since Mr. Navalny first fell ill on Aug. 20.
Mr. Navalny and his allies made modest gains in regional elections in Russia over the weekend, costing the ruling party its majority on the City Council in Novosibirsk, a Siberian industrial hub that is Russia’s third-largest city.
Moscow, which has declined to cooperate with German and European requests to shed light on the poisoning, has instead been pressing Berlin to share its findings and hospital reports about Mr. Navalny’s health.
Russia recently made an official request for mutual assistance in the case. The German government, acting according to protocol, instructed the Berlin prosecutor’s office to consult with Mr. Navalny. But Mr. Navalny declined on Monday to authorize the sharing of his files with the Russian authorities.
Leonid Volkov, Mr. Navalny’s chief of staff, who is in Berlin, said on Tuesday that Mr. Navalny would not be cooperating with a Russian investigation. He said that Mr. Navalny’s team was talking to German officials about the government’s response to Russia and that they welcomed the clarity with which German and other European officials had condemned the poisoning.
“The E.U. has taken a strong, a harsh position,” Mr. Volkov said. “They are using unusual wording in this case, which is a good sign that they might be prepared to go a step further.”
German officials now say they have almost no doubt that the Russian state was behind the poisoning of Mr. Navalny.
The German government said on Monday that laboratories in France and Sweden had confirmed that the substance used to poison Mr. Navalny was a form of the nerve agent Novichok. The results match Berlin’s own findings and provide additional confidence of state involvement, as Western intelligence agencies have assessed that only the Russian government was likely to have access to such a weapon.
German officials and others have said that any use of the nerve agent would violate the Chemical Weapons Convention, to which Russia is a signatory.
But even as patience with President Vladimir V. Putin is running thin, Berlin is struggling to determine how exactly to respond. Some have suggested canceling the Nord Stream 2 pipeline, a nearly completed, $11 billion project to carry natural gas from Russia to Germany.
So far, however, the German government, its European allies and the United States have not taken any action other than raising the prospect of imposing additional sanctions on Russia.
Katrin Bennhold reported from Berlin, and Michael Schwirtz from London.