Police in Oakland, Calif., and Atlanta clashed with Occupy Wall Street protesters on Tuesday.

In Oakland, police in riot gear sprayed the crowd with several rounds of tear gas after demonstrators began pelting them with rocks, bottles, firecrackers and paint.

"We had to deploy gas to stop the crowd," acting Police Chief Howard Jordan told reporters late Tuesday evening, the Associated Press reported.

Oakland police said the protesters, numbering about 500, had been asked to leave several areas in downtown Oakland where they had camped for weeks, including near City Hall.

"The city remains committed to respecting free speech, as well as maintaining the city's responsibility to protect public health and safety," Oakland police said in a statement, CNN reported.

In Atlanta, Mayor Kasim Reed dispatched envoys to protesters in the city's Woodruff Park "to see if we can find a way to resolve this amicably."

In both cities, protesters determined to defy police by refusing to leave wound up in jail.

The Occupy Wall Street protests, which began in Manhattan in September, spread like wildfire to cities worldwide, causing some speculation as to who is organizing and funding the "leaderless" movement.