Shares inBritish AirwaysparentIAGfell 4% in early trading on the London Stock Exchange this morning, the first day the UK markets had opened since the UK carrier's services were wrecked by its IT systems failure on 27 May.

BA services were decimated by the IT failure, which the airline attributed to a power cut and failure of back-up systems. While its IT systems were restored, delays and cancellations continued on 28 and 29 May.

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"Our IT systems are now back up and running and we will be operating a full flight schedule atHeathrowandGatwickon Tuesday 30 May," the airline said today, adding it is continuing to work to reconcile missing bags with customers.

Neither BA norIAGhas yet outlined the financial cost of the disruption.

After the decline of 4% in early trading on the London Stock Exchange,IAGshares climbed a little and were down just over 3% at �5.96 as of 09:00 local time.

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In a round of interviews on 29 May BA chief executive Alex Cruz dismissed suggestions from the GMB union that the failure was related to the recent outsourcing of IT jobs. "There are no redundancies or outsourcing taking place around this particular piece of hardware," Cruz told BBC news.

BA is the latest carrier to suffer disruption from a major IT failure.Southwest AirlinesandDelta Air Lineshave both faced major disruption in the last year as a result of IT failures attributed to power outages.