 -- British Airways CEO Alex Cruz said he was "profusely sorry" for Saturday's worldwide computer outage that stranded thousands of passengers.

In an interview that aired on the BBC, Cruz said that the airline will be back to operating 95 percent of its flights from London's Heathrow and Gatwick airports on Monday.

He added that a power surge was to blame for the outage and reiterated that there is no evidence of any kind of cyber attack.

An investigation is underway to learn why backup systems didn't kick in, Cruz said.

A British Airways spokesperson told ABC News on Monday, "The power supply issue was at one of our U.K. data centers local to the Heathrow area."

British Airways, which is part of the broader International Airlines Group, canceled all flights from Heathrow and Gatwick on Saturday after the company suffered a colossal IT failure.

British Airways canceled another 27 flights and had 117 more delayed on Monday. Its sister airlines in Spain -- Iberia and Air Nostrum -- canceled more than 320 flights on Monday, according to data from flight tracker FlightAware.com.

The airline is urging customers to check that their flight is operating before heading to the airport.

British Airways is expected to run a full schedule Tuesday at Heathrow, the airport announced on Twitter.

The outage came amid a busy travel weekend, as Monday is a holiday in both the United Kingdom and the United States.

"We are extremely sorry for the inconvenience this is causing our customers during this busy holiday period," British Airways said in a statement on Saturday.

ABC News on Saturday observed thousands of delayed passengers at one of British Airways' terminals at Heathrow. Some said they had never been alerted that their flights had been canceled.

ABC News' Matt Gutman contributed to this report.