A sign towards Salisbury District Hospital is seen after Yulia Skripal was discharged, in Salisbury, Britain, April 10, 2018. REUTERS/Peter Nicholls

MOSCOW (Reuters) - Russia’s Foreign Ministry said on Thursday that Britain should prove that poisoned former double agent Sergei Skripal and his daughter are not being held hostage.

Spokeswoman Maria Zakharova said that the Skripals were isolated by British authorities and no one has seen them for over a month.

Zakharova added there were doubts that a recent statement by Yulia Skripal was authentic.