Anti-Islamic material has been distributed to homes in south and east Belfast.
The leaflet was received by residents in the lower Ravenhill Road area and purported to be from a group called Generation Sparta, warning against the 'Islamification' of Northern Ireland.
It appears professionally produced and contains a number of racist messages, one of which calls for Catholics and Protestants to unite against "a common threat from fanatical Islamists" and that "Protestants and Catholics bled for this land, not Islamists".
It singles out Sinn Fein and the Alliance party for supporting immigration.
Police received a report on Wednesday that the leaflet had been delivered to an address in the area earlier in the week.
Chief Inspector David Moore said: "We are treating this as a hate incident at present and we are making a number of enquiries.
"The Police Service of Northern Ireland continues to make it clear that hate crime, in any form, is unacceptable.
"Each of us has a responsibility to ensure that we live in a society where diversity is respected. We in PSNI are working with our partners across the public, private and voluntary sectors to provide reassurance, support to victims and promote tolerance and respect for all cultures and identities."
Speaking to BBC Radio's Good Morning Ulster programme, local resident Meg said police had spoken to the neighbours and people in the area opposed to the leaflet's message.
This insane and terrifying pamphlet was posted through my door yesterday wtf pic.twitter.com/vHWJadJej5— Meg Brad (@MegMog95) April 3, 2018
DUP MLA Christopher Stalford wrote on Twitter he was raised on Carrington Street at the bottom of the Ravenhill Road, and the material in the leaflet does "not speak for the people who live there".
South Belfast MLA Mairtin O Muilleoir has described the material as "fascist and Islamophobic", saying his party is targeted for its commitment to "a diverse, inclusive and pluralist society".
"Sinn Fein unequivocally condemns hatred of this kind," he said.
"I have reached out to Muslim community leaders in south Belfast in an attempt to allay any concerns raised by this incident.
“I am calling on all communities, and all political leaders in the targeted areas, to publicly condemn this hatred."