Poker can be a money spinner for both companies and players

Operating profit climbed 67% to $319.3m (�169m) in the six months to 30 June, compared with $190.8m a year earlier. Sales jumped 51% to $661.9m, it said.

Partygaming said that its business outside of the US was growing quickly.

That may help reassure investors concerned that gaming companies are to be targeted by US prosecutors as they question the legality of betting.

However, shares in the group plunged nearly 10% on news that the chairman of rival gaming group Sportingbet had been arrested in the US on his way to Costa Rica.

'Cash machine'

The issue of online betting in the US came into focus after authorities there arrested the head of Antigua-based gambling company Betonsports in July.

"Whilst regulatory uncertainties continue, the board remains confident about the group's full year prospects," said Partygaming boss Mitch Garber.

"The story remains the same - exponential growth in income but the shares overshadowed by the threat of the US regulatory position," said Richard Hunter of Hargreaves Lansdown Stockbrokers.