SEATTLE — Demonstrators at small but raucous gatherings around the country Saturday raised the specter that extremist interpretations of Islamic law might somehow spread across the U.S., but many of the rallies drew even more boisterous counter-protests by people who called such fears unfounded.

Hundreds of counter-protesters marched through downtown Seattle, banging drums, cymbals and cowbells behind a large sign saying "Seattle stands with our Muslim neighbors." Participants chanted "No hate, no fear, Muslims are welcome here" on their way to City Hall, where dozens of anti-Shariah protesters rallied.

A phalanx of bicycle police officers kept the sides separated during the sanctioned events, but authorities said a large fight broke out after the gatherings concluded. Police used tear gas to disperse rowdy demonstrators and arrested three people for obstructing law enforcement.

The rallies, held in more than two dozen U.S. cities, were organized by ACT for America, which claims Islamic law is incompatible with Western democracy.

The organization said it opposes discrimination and supports the rights of those subject to Shariah. However, the Southern Poverty Law Center, which tracks hate groups, calls it the largest American anti-Muslim group.

"I don't believe Islam can peacefully co-exist with the Constitution," said Seattle anti-Shariah demonstrator Aaron Bassford, 29. "We need unity in this country under no ideology and no banner except the Constitution of the United States of America."

But the overwhelming majority of Muslims don't want to replace U.S. law with Islamic law, known as Shariah, and only "radical extremist groups" would call for that, said Liyakat Takim, a professor of Islamic studies at McMaster University in the Canadian city of Hamilton, Ontario.

"The Quran allows slavery. So does the Old Testament. That doesn't mean we allow it today, too," Takim said. "Laws are amenable to change."