MOSCOW, Jan 18 (Reuters) - Russian state prosecutors on Monday asked a court to jail Kremlin critic Alexei Navalny for 30 days, Ivan Zhdanov, a Navlany ally wrote on Twitter.

Western nations have urged Russia to immediately free Navalny, who was detained late on Sunday at a Moscow airport after flying home for the first time since he was poisoned last summer. (Reporting by Anton Zverev/Vladimir Soldatkin; Writing by Alexander Marrow Editing by Andrew Osborn)