Research in Motion’s co-chief executives apologized to BlackBerry users Thursday morning and said the smartphone’s services had been fully restored.

Users should be receiving e-mails and text messages on their devices Thursday as the company works through the backlog of undelivered messages, Jim Balsillie and Mike Lazaridis told reporters during a conference call.

Lazaridis said that some users may have to remove their batteries and restart their phones to reactivate automatic syncing.

They confirmed that it was the largest outage that BlackBerry’s systems had ever seen.

Lazaridis said that a problem with system hardware caused a backlog of data to build up in the company’s European servers. The company’s backup systems also failed, resulting in a cascading failure that started in Europe and spread across the world.

Lazaridis said that the company is auditing its process and investigating why the backup systems failed. He declined to comment on how long it will take for the company to analyze the root cause of the failure.

He said that it was most likely a hardware failure, but it will take time to determine why the back-up systems did not work properly and how the company can prevent similar problems in the future.

Balsillie said that the company will next turn its attention to compensation for consumers. “We’re going to work very hard to win their trust back, 100 percent,” he said.

The company will continue to provide service updates on its Web site throughout the day.

Related stories:

BlackBerry outages spread to the U.S.

BlackBerry outage spurs customers to end their phone relationship

Apple iPhone 4S review: It’s the software that’s a surprise