“There has been some improvement in the symptoms caused by the inhibition of cholinesterase activity,” the German capital’s Charite hospital, where Navalny arrived last Saturday, said in a statement.

Navalny, 44, has been one of the fiercest opponents of Russian President Vladimir Putin during the past decade. He fell ill on a domestic flight in Russia on August 20.

The Charite hospital said on Monday there were indications to back claims that he was poisoned.

Navalny remains in the hospital’s intensive care unit, where he is being kept on a ventilator.

“While his condition remains serious, there is no immediate danger to his life,” the Charite statement said, adding that it was however too early to gauge potential long-term effects.