President Donald Trump's order to bar travellers from seven Muslim-majority countries is not the best way to protect America from terrorists and can spread "anxiety and anger", UN chief Antonio Guterres has said and called for lifting the ban.

"In my opinion this is not the way to best protect the US or any other country in relation to the serious concerns that exist about possibilities of terrorist infiltration. I don't think this is the effective way to do so. These measures should be removed sooner rather than later," Guterres told reporters here, responding to questions on the travel and refugee ban imposed by the US.

The UN Secretary-General emphasised that it is important not to have measures that "spread anxiety and anger" because then "we help trigger the kind of recruitment mechanisms that these (global terrorist) organisations are now doing everywhere in the world," he said.

Guterres cautioned that banning people and refugees from entering other nations will not ensure that terrorists will not infiltrate as the extremist groups could circumvent measures and look at other ways to target nations and their citizens.

The international community is dealing with "very sophisticated global terrorists originations", he said, adding that if terror groups want to attack any country they will not send people with passports from "hotspots of conflict".

"They might come with passports from the most developed, credible countries or use people that have been for decades present in the country itself," he said.

On the possibility that the Trump administration will cut US funding to the UN, Guterres said he will not comment on something that has not yet occurred.

"Sometimes we talk too much about things that have not happened and when we talk too much about things that have not happened, you trigger the happening of those things. I will not be making comments on possibilities to enhance those possibilities to possibly be a reality," he said.

Guterres stressed he will do "whatever" he can to prove the added value of the UN, to recognise the UN needs reforms and to believe that those reforms will be the best way to guarantee the support of all member states including US and its new administration.

On the indefinite ban on Syrian refugees entering the US, Guterres said resettlement of refugees is in many situations the only possible solution.

"The US has always been in the forefront of refugee settlement and Syrians at the present moment have more dramatic needs in the world. I strongly hope that the US will be able to reassess its very solid refugee protection in resettlement and I hope Syrians will not be excluded in that process," he said.

Trump's controversial executive order, signed on Friday, halted the entire US refugee programme for 120 days, indefinitely banned Syrian refugees, and suspended all nationals from seven Muslim-majority countries — Iran, Iraq, Libya, Sudan, Yemen, Syria and Somalia.