German doctors treating Russian opposition leader Alexei Navalny after he was poisoned with a nerve agent have detailed the case in an article for a major medical journal.

Berlin's Charite hospital said Mr Navalny had given his permission for the article to be published in The Lancet journal.

He fell ill suddenly on a domestic flight in Russia on August 20. After an emergency landing and treatment at a Siberian hospital in Omsk, two days of political wrangling ended with Mr Navalny being flown to Berlin on a private air ambulance on August 22.

The European Union imposed sanctions on six Russian officials and a state research institute after tests by the Organisation for the Prohibition of Chemical Weapons established that he had been exposed to Soviet-era nerve agent Novichok.

The Kremlin, which denies involvement in the poisoning, has hit back with its own sanctions against EU officials.

In their journal article, Charite doctors detailed the course of Mr Navalny's illness and treatment with a variety of drugs to address his symptoms and the underlying medical condition.

As his condition improved, he was brought out of a medically induced coma and doctors determined that difficulties understanding speech and speaking he had initially showed after waking up disappeared after three weeks.

"At the last follow-up visit on day 55, we found near-complete recovery of neurological, neuropsychological and neurophysiological findings without evidence of polyneuropathy," they wrote.

It is the first clinical case study detailing a Novichok poisoning, although the symptoms and treatment are similar to those for exposure to organophosphorus pesticides, which claim more than 100,000 lives in Asia each year.

Mr Navalny's doctors noted that their patient "had a very favourable outcome" and attribute it to the swift treatment he received in Russia.

Last week, a joint investigation by research group Bellingcat and several media outlets alleged that operatives from Russia's FSB domestic security agency had followed Mr Navalny during his trips since 2017.

Mr Navalny, who is convalescing in Germany, this week posted a video of a phone call to one of the alleged operatives, who said the poison was applied to his underwear. The FSB has branded the call a fake.