Citizens of the tiny city state of Singapore have the most powerful passports in the world, it has been revealed.

But the usefulness of a US passport has fallen slightly since President Donald Trump took office, with Turkey and the Central African Republic becoming the most recent countries to revoke visa-free entry for holders.

A new ranking of world passports by website Passport Index found that citizens of Singapore can travel to the highest number of countries visa-free.

It took the top spot after Paraguay removed restrictions which had been in place for Singaporeans.

The 3.4m holders of Singaporean passports can now travel to 159 countries without a visa – or by obtaining a visa on arrival.

Germany is in second place, with citizens able to visit 158 countries without obtaining a visa first, while Sweden and South Korea are tied in third place.

The UK is tied in fourth place along with Denmark, Finland, Italy, France, Spain, Norway, and Japan.

Brits can travel to 156 countries visa-free. The US is in 6th position along with Canada, Ireland and Malaysia.

(Getty Images (Getty Images)

Passport Index ranks passports in real time, based on the cross-border access a holder has.

It was developed by a Canada-based global consultancy firm called Arton Capita.

Philippe May, managing director of Arton Capital's Singapore office, said: “For the first time ever, an Asian country has the most powerful passport in the world.

“It is a testament of Singapore's inclusive diplomatic relations and effective foreign policy.”

The least powerful passport continues to be Afghanistan, with just 22 countries allowing visa-free access to its residents.