John Kelly said the existing rules – which do not require Europeans to obtain a visa - should be reviewed amid concerns over terrorism.
When asked by about the current visa waiver, Kelly said: “We have to start looking very hard at that programme.”
He added that he was not considering scrapping the system entirely but said the current practice needed a review.
"Not eliminating it and not doing anything excessive…but look very hard at that programme,” Kelly was reported by CNNMoney as saying during a speech in Washington.
Currently, UK and European citizens staying for less than 90 days can travel to America on an Esta.
Around 14 million Europeans used it to travel to the US in 2015.
According to The Independent, Kelly said he feared Isis fighters were using the visa-waiver system to enter into the US - warning America was the “Super Bowl in terms of terrorists”.
In 2015, the White House tightened rules so that nationals of visa-waiver countries who had been to Iran, Iraq, Libya, Somalia, Sudan, Syria, or Yemen on or after March 1, 2011, were no longer eligible.
In March this year, the European Parliament voted to end visa-free travel for Americans within the EU after the US failed to agree visa-free travel for citizens of five EU countries – Bulgaria, Croatia, Cyprus, Poland and Romania.
