"This was unfortunately the largest (outage) we've experience.''
"I want to apologise to all of the BlackBerry customers we've let down,'' he said.
"You expect better of us. I expect better of us. Our inability to quickly fix this has been frustrating.''
RIM said an initial technical failure had prompted a build-up of messages in its network that snowballed around the world, affecting many of the firm's 70 million subscribers.
The hardware failure reportedly started at the company's British hub in Slough, a town west of London.
Lazaridis said the company was taking "immediate and aggressive steps'', including with its suppliers responsible for the design and manufacture of the "core switch'' blamed for the outage, "to minimise the risk of something of this magnitude happening again''.
Its failure "caused a cascade failure in our system'', he explained. "There was a backup switch but the backup didn't function as intended and this led to a backlog (of messages) in the system.
"The failure in Europe in turn overloaded systems elsewhere.''
However, Lazaridis conceded: "We (still) don't know why the switch failed in the particular way it did,'' and why the backup system also failed.
RIM announced on Monday that the issue had been resolved, but the glitches spread, sparking outrage from BlackBerry users worldwide.
The problems represent a PR nightmare for RIM, which has faced weaker sales of the BlackBerry compared with smartphones made by Apple or those running Google's Android software.
The timing is particularly bad ahead of Apple's launch on Friday of the latest iteration of its top-selling smartphone, the iPhone 4S, in key world markets.
Major Asia-Pacific markets such as Australia, Japan and South Korea have been unaffected for the most part, but irate users in China and India reported widespread outages this week.
Much of the anger has been caused by a lack of information about the problems, which Lazaridis acknowledged. In a video message earlier, he promised to update users more frequently through its websites and social media channels about future woes.
As a result of this week's outage, Lazaridis also said RIM is "very concerned'' about the loss of customer confidence and sales.
RIM shares fell 2.4 per cent on the Nasdaq and 1.8 per cent in Toronto in morning trading, after dropping nearly 60 percent since January.
Alain Chung, an analyst with investment firm Claret, said the BlackBerry remains for most business users "the best smartphone on the market''.
Outages are not RIM's biggest problem, he said. Rather, its lacklustre marketing strategy and delays in launching a new operating system, QNX, are of greater concern.
- AAP
