Research In Motion, makers of the popular BlackBerry smartphone, said Tuesday that a recent three-hour service disruption has been linked to a system upgrade performed to increase the overall capacity of the company's data and e-mail services.

RIM, which has been experiencing rapid growth in subscribers, said capacity-boosting upgrades are done regularly, and similar work had been done before without a hitch. This time, however, the upgrade left subscribers with only intermittent access to e-mail and other data services between 3:30 p.m. EST and 6:30 p.m. EST Monday.

"RIM's early investigation of the service interruption that occurred on Monday points to a problem with an internal data routing system within the BlackBerry service infrastructure that had been recently upgraded," the company said in an e-mailed statement. "The upgrade was part of RIM's routine and ongoing efforts to increase overall capacity for longer term growth."

RIM has been trying to expand the central hub through which all e-mails flow in order to keep up with the rapid growth in subscribers. In its last quarter, RIM added 1.65 million BlackBerry subscribers, bringing its worldwide total to 12 million.

Zenprise, a maker of service-management software for companies using the BlackBerry, said its own diagnostic tests showed that one of two Internet protocol addresses used to connect to the RIM network in North America had refused to let connections through, As a result, people were unable to access the service. Users connecting to the other IP address did not experience any interruptions, Zenprise said.

The outage is the second widespread service problem reported by RIM in less than a year. In April, a more serious breakdown centered at the company's primary network operating center for North America left 8 million subscribers unable to send or receive e-mails. The center is located at RIM headquarters in Waterloo, Ontario.

The failure raised questions as to whether RIM, which has chosen to keep its entire network infrastructure in-house and in relatively centralized form, can continue to scale to meet demand for BlackBerry services.

Lately, RIM has been pushing the BlackBerry beyond businesses and into the consumer market. Rather than only supporting features for business, BlackBerry devices are available today with multimedia functions, such as music and video players, cameras, and social-networking software. More than a third of RIM's subscribers are classified as non-corporate or non-government.