Swansea's Alfie Mawson could be David Moyes' first key signing at West Ham. Photo by Athena Pictures/Getty Images

West Ham United are closing in on the signing of Swansea City defender Alfie Mawson, sources close to the Welsh club have told ESPN FC.

West Ham boss David Moyes has made signing a new central defender during January's transfer window a top priority and has identified Mawson as his top target.

Moyes is keen to bring in signings who have Premier League experience and Mawson fits the bill after impressing at Swansea following his arrival from Barnsley for around £5 million in the summer of 2016.

Mawson caught the eye at Swansea last season playing a key role in the Swans' survival in the Premier League and the England Under-21 international has been tipped for a call-up to the senior side.

The 23-year-old has been an ever-present for Swansea in the Premier League this season, but he has been unable to help them clear of the bottom of the table.

Swansea's plight at the bottom of the league and being without a manager has left them vulnerable to interest in their best players and West Ham are hoping to take advantage.

West Ham are prepared to pay a fee in excess of £20m plus add-ons to persuade Swansea to cash-in on the former Brentford and Wycombe defender.

The Welsh club are reluctant to lose Mawson as they battle against relegation, but they are aware they could use any funds from the defender's sale to strengthen the squad elsewhere.