The owner of high-end fashion brands Hobbs, Whistles and Phase Eight says it is investigating a cyber-security incident.

According to TFG London – the UK arm of retail conglomerate The Foschini Group – it identified an incident on Sunday affecting some IT systems and “specifically impacting our Phase Eight, Hobbs, and Whistles brands”.

“We are actively investigating and working with external cyber security specialists,” the company told BBC News in a statement.

Meanwhile, H&M is investigating a separate claim that it was attacked by a notorious hacking group.

TFG said its brands’ stores are operating as normal but some website capabilities may be unavailable, adding “we apologise for any disruption and will provide additional updates to our customers as appropriate”.

The retail group reportedly told customers in an email that it did not believe customers’ payment information had been affected by the incident.

“As our investigation continues, we will be working to identify if any sensitive information related to our customers was impacted,” it said.

The email, seen by news service PA, also said that those whose personal information had been impacted would be informed directly.

“We do not believe it is necessary to change your account login information at this time,” it added.

Beverley Griffiths, senior lecturer in security and resilience at Bucks New University told PA that this was “a clear sign that major brands are firmly in the crosshairs of cyber attackers”.

Fashion giants ranging from Adidas to Alexander McQueen have been targeted by cyber-criminals seeking to extort money by threatening to release customer data unless they are paid a ransom.

“No organisation is immune, so the real test of resilience is how quickly a business can detect an incident, respond and recover while keeping its customers informed,” Griffiths said – adding customers should stay “vigilant” and wary of suspicious messages.

Charlotte Wilson, head of enterprise at cyber-security firm Check Point, said attacks targeting retailers were “starting to look rather like buses… you wait for one, and suddenly three come along at once”.

She told the BBC that while it was too soon to ascertain how the incident affecting TFG London’s systems occurred, or whether it was related to other recent hacks, “the retail industry has some serious questions to answer about how exposed its systems have become”.