Khan put Medjadi down inside the first minute

The 20-year-old felled his opponent with a fierce right-hand punch and the Frenchman was unable to continue.

It was the Bolton boxer's 11th professional victory.

Khan's next fight will be on the undercard of the Joe Calzaghe-Peter Manfredo Jnr bill at Cardiff's Millennium Stadium on 7 April.

Interview: Amir Khan

Khan claimed afterwards the punch he had thrown was the best of his professional career.

I caught him round the chin and he just dropped Amir Khan

"Probably," he said. "I'm not going to get paid for overtime.

"His balance wasn't the best - every time you could see his left hand was dropping and I timed it perfectly.

"He was slower than me, I could see every shot. It felt good, I felt the power line through my arm. In my professional career it was my best shot.

"I didn't plan to finish it in the first round, I just came in and caught him with a right hand and he went down. I caught him round the chin and he just dropped."

Earlier on the card, Luton lightweight Graham Earl suffered defeat in an extraordinary interim WBO world lightweight title fight against Australian Michael Katsidis.

In a bruising encounter, Earl was saved by the bell at the end of round one after being floored twice in the final 30 seconds.

Earl was knocked down once more by a right cross early in the second and the towel was thrown in by his corner, only for referee Micky Vann to throw it back out of the ring and continue the fight.

The Briton then forced Katsidis to his knees, forcing his first count of the bout, but the Queenslander hit back viciously in the fourth prompting Earl's corner to retire their man at the end of the round.

Earl, 28, had been seen as a potential opponent for Khan but Katsidis extended his unbeaten record to 22 fights since turning professional in 2001.