A man has been arrested in the UK on suspicion of making a malicious social media post about the attacks that killed 49 people at mosques in New Zealand.
Greater Manchester Police (GMP) said the post was "making reference and support for the terrible events".
The arrested man is a 24-year old from Oldham.
GMP said where "people cross the line, we will take robust action, which may include arrest and prosecution".
The force said: "This is a very difficult time for people. The events in New Zealand have reverberated around the world.
"Many people are in deep shock and are worried. It is at times like this that, as a community, we stand together."
Brenton Tarrant, a 28-year-old Australian who described himself as a white supremacist, has been charged following the attacks during Friday prayers.
Social media firms and some news outlets have been criticised for sharing livestream footage of the attack and failing to address far-right extremism on their platforms.
In London, police have launched an investigation after a burning rag was found in a road near a mosque.
The cloth was extinguished by Metropolitan Police officers in Southall and sent for forensic examination. Nobody was injured.