LONDON, April 8 (Reuters) - The London Stock Exchange Group said on Thursday it was investigating a lengthy outage at its newly-acquired Refinitiv market data unit.

The outage at Refinitiv's Eikon platform for market prices began around 0730 GMT. Subscribers who rely on its data for trading currencies and other assets, said on Twitter they were unable to access prices.

"We're aware of an issue disrupting our service to customers," LSEG said in a statement.

"We are currently investigating the cause of the issue and working hard to resolve the problem. We apologise to customers for the disruption."

LSEG completed its $27 billion purchase of Refinitiv on Jan 29. Analysts had already expressed concerns last month that integration costs will be heavier and cover a longer period than had been expected.

Its shares have fallen 20% so far this year.

"Clearly this morning this is bad news for the group not to mention that clients have been left high and dry with no trading and loss of crucial market data," said Securequity sales trader Jawaid Afsar.

Thomson Reuters, owner of Reuters News, has a 15% stake in LSE Group.

LSE shares were up 1.07% at 08:59 GMT according to prices on Yahoo. (Reporting by Thyagaraju Adinarayan and Huw Jones; Editing by Rachel Armstrong and Jon Boyle)