United States President Donald Trump ordered authorities to step up an “already extreme vetting” process for foreign travellers after a man driving a truck killed eight people in Manhattan on Tuesday evening.

The police identified the man as a 29-year-old immigrant who came to the US in 2010. Eleven people were injured in the incident, which authorities are calling a “terror attack”.

“I have just ordered Homeland Security to step up our already Extreme Vetting Program,” Trump said on Twitter . “Being politically correct is fine, but not for this!”

In another tweet, he called the man a “very sick and deranged person”. He also said that the US must not allow the Islamic State group to return or enter the country.

Soon after coming to power in January, Trump had signed an executive order to strengthen the screening process for foreign travellers, in what he called a measure against terrorism. He also tried to block travellers from specific countries – a step that met with legal resistance and global condemnation. His attempted travel bans were criticised as a ban on mainly Muslim countries.