LONDON (REUTERS) - Former England international footballer Adam Johnson was jailed for six years on Thursday, after being found guilty of sex offences involving an underaged 15-year-old girl.

Johnson, 28, who was sacked by Premier League club Sunderland in February, was convicted earlier this month of sexual activity with a child, having already admitted kissing and grooming the teenager.

"Adam Johnson exploited a young star-struck fan, actively grooming her over a number of months in single-minded pursuit of his own sexual gratification," said Gerry Wareham from Britain's Crown Prosecution Service, outside Bradford Crown Court in northern England.

"This situation had a devastating effect on the young victim and it is my sincere hope that she and her family will be granted the respect and space they deserve to recover and rebuild their lives."

The winger, who has played 12 times for England, began his career at Middlesbrough and also played for Manchester City before joining Sunderland for £10 million (S$19.3 million) in 2012 on a four-year contract.

He had been a regular for the north-east side this season until the start of his trial and scored in his last appearance in a 2-2 draw with Liverpool last month.

Johnson was suspended by Sunderland in March 2015 after being arrested but two weeks later the club lifted the ban.

Sunderland's chief executive Margaret Byrne resigned two weeks ago over her role in the decision to allow Johnson to continue playing for the team.