LONDON (AFP) - British bank HSBC fired six staff after they performed a mock ISIS-style execution video during a team-building day out and posted footage online, a spokesman confirmed on Tuesday.

The bank described the video, showing staff members in balaclavas holding a fake knife over a kneeling man in an orange jumpsuit, as "abhorrent".

"We took the decision to sack the individuals involved," a spokesman for the bank said.

"This is an abhorrent video and HSBC would like to apologise for any offence caused."

The employees filmed the video on an HSBC team-building day and published it on Instagram before deleting it, according to newspaper The Sun, which published screen shots of the clip.

In it, a kneeling man in a jumpsuit is held by the shoulders while a colleague wields a coat-hanger like a knife above him, as though preparing to cut off his head.

One staff member shouts "Allahu Akbar" (God is the greatest in Arabic) during the clip, according to The Sun.

The staging recalls gruesome beheading videos released by the Islamic State in Iraq and Syria (ISIS) group, which has executed over 3,000 people in Syria in the year since it declared an Islamic "caliphate" in Syria and Iraq, according to the Syrian Observatory for Human Rights.

ISIS killed a series of international hostages dressed in orange jumpsuits, including British aid workers David Haines and Alan Henning, in videos that caused shock when they were released last year.

HSBC has recently weathered a string of bad publicity, including allegations its Swiss private banking arm helped wealthy clients dodge tax, and fines by regulators for attempting to rig foreign exchange markets.