ENGLAND (REUTERS) - Liverpool have signed left-back Andy Robertson from Hull City on a long-term contract, while midfielder Kevin Stewart has moved in the opposite direction, the Merseyside club said on Friday.

Financial details of the Robertson deal were not disclosed, but British media reported that Liverpool had paid Hull £10 million (S$17.7 million) to secure his signature.

"It feels a wee bit surreal just now," Robertson told Liverpool's website. (liverpoolfc.com)

"Obviously I'm delighted. There's been a lot of speculation over the last couple of weeks, but I'm glad that the deal's finally been done and I'm a Liverpool player."

The 23-year-old Scotland international made 116 appearances and scored five goals for Hull after joining from Dundee United in 2014.

His arrival increases Liverpool manager Jurgen Klopp's options at the left-back position.

The German deployed midfielder James Milner in the position for most of last season after Spaniard Alberto Moreno fell out of favour.

"For Andrew, this is another big step on what has been a quite incredible personal journey in a very short space of time," Klopp said.

"He has experience of... the Premier League, and he has the mentality and quality to get even better."

Klopp said Robertson's arrival would increase competition for the left-back spot.

"Obviously, James Milner did very well for us last season there and can play most positions on the football pitch. Alberto Moreno looks really good in pre-season (training) and we have Jon Flanagan back, who can play left or right full-back."

Stewart, who is also 23, joined Liverpool from Tottenham Hotspur in 2014, and made 20 first-team appearances for the Merseyside club.

He has joined Hull, who were relegated from the English top tier last season, on a three-year contract.