The Advertising Standards Authority (ASA) has revealed that children were left distressed after seeing ads for a horror film on YouTube .

Three parents contacted the ASA after their children saw ads for Insidious: The Last Key - rated 15 in the UK.

One ad for the film was shown before videos of songs from Frozen, instructions for building a Lego fire station and a clip from the cartoon PJ Masks.

The ASA has upheld the complaints.

In a second ad, the ASA said a young woman was seen "lying on a floor immobile, bloodied and distressed while a humanoid creature crept towards her and then probed at her with claw-like fingers and pierced her skin".

Screaming women

Further horror-themed imagery followed, including a sequence of women screaming.

This ad played before two videos of Minecraft, a game popular with children.

Sony Pictures and Sony-owned Columbia Pictures, which promoted the film, told the ASA they had excluded unknown audiences and children from their targeting.

The BBC understands that a follow-up probe by Sony indicated that YouTube's content categorising algorithms were at fault.

The Google-owned streaming service, however, said that advertisers were responsible for own their campaigns.

The video site added the ads had not appeared on YouTube Kids, an app aimed specifically at children that offers a filtered selection of YouTube content.

"We considered the ads were unsuitable for children because they were excessively frightening and shocking, and were likely to cause fear and distress," the ASA said in its ruling.

The ASA also received three complaints from adults who found the ads unduly distressing. And it noted that the ads had appeared before unrelated content, with no warning and could not be skipped until five seconds had elapsed.

The regulator has told Sony Pictures to ensure that future ads are appropriately targeted.

The firm declined to comment.

But the BBC understands that it is now limiting its ads for mature content to a pre-vetted list of safe YouTube channels.