LONDON (Reuters) -Britain's National Health Service said on Monday that data had been published online following a highly disruptive ransomware attack on a medical diagnostics service used by several major London hospitals earlier this month.

NHS England said the Synnovis diagnostics service - a partnership between the hospitals and German company Synlab - would carry out further work to understand the full scale of the data breach and how patients had been affected.

"Synnovis has now confirmed through an initial analysis that the data published by a cyber crime group has been stolen from some of their systems," NHS England said.

NHS England said it might be some weeks before it was clear which individuals have been impacted.

"At present, Synnovis has confirmed there is no evidence the cyber criminals have published a copy of the database (Laboratory Information Management System) where patient test requests and results are stored, although their investigations are ongoing," NHS statement said.

The BBC reported last week that the criminal group behind the attack has been trying to extort money from Synnovis and had threatened to publish data if it was not paid. The BBC said it had seen a sample of data that included patients' names, dates of birth, NHS numbers and descriptions of blood tests.

Services at large London hospitals including Guy's, St Thomas' and King's have been disrupted following the attack.

"Local health systems will continue to work together to manage the impact on patients with additional resources put in to ensure urgent blood samples can still be processed, while laboratories are now able to see historic patient records," NHS England said.

(Reporting by Muvija M; editing by David Milliken)

By Muvija M