GOP presidential candidate Donald Trump repeated his call Saturday for surveillance of mosques and a database on Syrian refugees coming into the United States, following a series of overseas terror attacks connected to Islamic extremist groups.

“I want surveillance of these people and of certain mosques,” the front-running Trump said at a campaign event in Birmingham, Ala. “We’ve had it before, we will have it again.”

The New York police department kept surveillance on mosques after the Sept. 11, 2001, attacks. But the controversial program was ended in 2014.

Trump also said he witnessed thousands of people across the Hudson River in New Jersey cheered when Islamic extremist hijackers during the 9/11 attacks crashed two U.S. airlines into the twin World Trade Center towers, toppling the skyscrapers in lower Manhattan and killing thousands.

“Something is going on,” he said.

Trump also said he wants a database on all Syrians refugees coming into the U.S., following the recent, deadly attacks in Paris in which one suicide bomber allegedly came from war-torn Syria and entered France by foiling Europe’s refugee vetting system.

He appeared to clarify a comment earlier this week about such a database, making clear it would apply to all Syrian refugees being resettled in the U.S.

Trump, among the most outspoken of the 2016 presidential candidates on illegal immigration, also said that if elected he would make Syrians resettled in the U.S. leave the country.

“They’ll go back,” he said.

When announcing his White House bid this summer, Trump vowed to build a wall along the U.S.-Mexico border to stop the flow of illegal immigrants including “rapists” and “drug dealers.”

Despite the backlash, Trump continues to tout the plan, to the support of his conservative base, especially in the wake of the recent terror attacks.

President Obama says his administration will continue to accept Syrian refugees, include 10,000 more through 2016. However, Congress doesn’t appear to fully support the plan, amid voter fears that the refugee vetting process is not as thorough as needed.

On Thursday, the GOP-led House, with the support of 47 Democrats, voted in favor of tighter regulation on allowing refugees into the country.

Fox News' Chris Snyder contributed to this report.