BRUSSELS (AFP) - Belgian police offered a virtual bowl of pet food to Internet cats on Monday (Nov 23) to thank social media users for agreeing to pause their posts during a major anti-terrorism operation in Brussels.

"For the cats that helped us last night... help yourselves!" Belgian police said on their Twitter account, with a photo of a metal bowl with the police logo in French and Flemish, filled with cat food pellets.

It was retweeted more than 4,400 times in French and 1,400 times in Flemish.

The Twitter hashtag #BrusselsLockdown went viral on Sunday night when social media users posted pictures of their feline friends - a light-hearted response to an official request from police not to put information about their operation on the Internet.

There were pictures of cats with guns, cats looking scared, cats with helmets on and even a surreal picture of two Star Wars stormtroopers riding hover scooters shaped like cats.

The cat photos were a whimsical break from a tense situation, with Brussels under security lockdown since Saturday morning after the government said there was a "serious and imminent threat" of attacks like those in Paris on Nov 13.

Key Paris suspect Salah Abdeslam, who is believed to be in Belgium, remains at large despite police arresting 21 people overnight.