New York Attack: Donald Trump Says We Must Not Allow ISIS to Return to US

Washington: America must not let Islamic State jihadists return to or enter the US after they are beaten overseas, President Donald Trump said Tuesday, hours after a deadly New York attack.

"We must not allow ISIS to return, or enter, our country after defeating them in the Middle East and elsewhere. Enough!" Trump tweeted.

New York Mayor Bill de Blasio called the attack an "act of terror" but authorities have not definitively linked the suspect who has detained afterwards to IS.

Eight people were killed and numerous others wounded when the suspect rammed a pickup truck into pedestrians in Lower Manhattan and collided with a school bus, officials said.

Trump earlier decried the attack as an act of madness.

"In NYC, looks like another attack by a very sick and deranged person," Trump tweeted.

"Law enforcement is following this closely. NOT IN THE U.S.A.!"

IS has been dealt a string of defeats across Iraq and Syria in recent months, with authorities worried that fleeing foreign fighters might return home.

Donald Trump had also ordered more robust "extreme vetting" of travellers coming into the United States following the first deadly attack in New York blamed on terror since the September 11, 2001 strikes.

"I have just ordered Homeland Security to step up our already Extreme Vetting Program. Being politically correct is fine, but not for this!" Trump tweeted.