Liverpool manager Jurgen Klopp has been asked to provide written observations to the Football Association over his comments about referee Kevin Friend, Press Association Sport understands.

The Reds lost a little momentum in their Premier League title bid after a 1-1 draw at West Ham on Monday night, when replays showed Sadio Mane's opener should have been cancelled out for offside in the build-up.

Michail Antonio equalised for West Ham minutes later but Klopp suggested Friend had found out about his assistant's mistake at half-time and that the official's decision-making thereafter may have been compromised as a result.

Klopp told Sky Sports: "We had good moments, coming through the channels and scored the goal, which I've now been told is offside. This explains a little bit the second half, because I think the referee knew at half-time.

"He knew it for sure at half-time, and then you saw a lot of strange situations. They were not decisive but just rhythm-breakers. That obviously didn't help us.

"There were so many situations where it was 50-50 or 60-40... [he gave a] free-kick for the other team."

His remarks have attracted the attention of the FA, which has sought Klopp's opinion on the matter.

The Merseysiders could have snatched a late winner through substitute Divock Origi, who appeared to be in an offside position before going clean through only to see his effort saved by Hammers goalkeeper Lukasz Fabianski.

Liverpool increased their lead at the top of the standings to three points but Manchester City have the chance to leapfrog Klopp's men by winning at Everton on Wednesday night.