Border agents said Wednesday they arrested an unusually large group of illegal immigrants crossing through the western Arizona desert in what authorities said is proof that increased border technology is working.

Border Patrol surveillance video operators Friday morning spotted a group of more than 100 people walking just north of the Mexico border about 15 miles west of Lukeville, Ariz., Agent Eric Cantu said.

When agents responded, Cantu said they were able to arrest 22 people but the rest of the group scattered.

A helicopter team found much of the group hiding in thick brush, and agents arrested 106 additional illegal immigrants. The smugglers and other suspected illegal immigrants may have gotten away, Cantu said.

The 128 men who were apprehended have either been returned to Mexico or were jailed because of prior convictions.

The Border Patrol's Tucson sector typically sees such large groups of border crossers no more than once or twice a year, Cantu said. Illegal immigrants typically travel in groups of five to 15, he said, because larger groups are much easier to detect.

"Before in remote areas we didn't have the technology or infrastructure or personnel to actively patrol and monitor the more remote areas," he said. "The larger groups are easier to spot so they're getting rarer and rarer. We're getting to the point where it's almost impossible to cross in groups so large."

Cantu said it didn't make sense why smugglers attempted to take last week's large group into the U.S.

He said several smugglers likely were with the group but either got away or successfully blended in with the immigrants and went undetected as smugglers.

"Normally smugglers are the first ones to run, and they'll abandon the group and leave the group to fend for themselves," Cantu said.