TORONTO (Reuters) - Law enforcers have broken up an international ring that smuggled more than 100 people from several countries across the Canada-U.S. border and have made 17 arrests in four cities, officials said on Tuesday.

Police said they expected further arrests in the case, after the group smuggled people from Canada to the United States and from the United States to Canada.

They said cooperation between U.S. and Canadian agencies was unprecedented, taking advantage of rules brought in after the September 11 attacks that tightened security along the world's longest unguarded border -- some 8,890 km (5,560 miles) including the border with Alaska.

"We are alleging that over the last two years, this group was responsible for the majority of migrants that were smuggled into the U.S. (from Canada)," said Michele Paradis, a spokeswoman with the Royal Canadian Mounted Police.

"They were being hidden in trunks of cars, they were being put on railway cars, they were put in the backs of transport trucks and there were occasions where small boats were used."

Paradis said the illegal migrants were from China, Korea and Eastern Europe. Twenty-four were arrested while trying to enter Canada from the States, and at least 74 were caught trying to cross into the United States.

"The smugglers themselves are not the least bit concerned for the safety of the migrants at all," Paradis said. "They're only concerned about one thing, and one thing only, and that's the amount of money they can make."

The two-year international investigation involved the Mounties, part of the U.S. Department of Homeland Security and Canada's Border Services Agency.

Greg Palmore, of the Department of Homeland Security's Immigration and Customs Enforcement section, said the new rules had helped law enforcers on both sides of the border work closely at a high level.

"It made the border invisible," he said. "It allowed us to work together without the barriers that would normally be in place on a border."