ROME, Aug 4 (Reuters) - The Italian government is committed to fully collecting revenues stemming from a windfall tax imposed on energy companies, Prime Minister Mario Draghi said on Thursday.

Many Italian energy companies appear not to have paid an initial windfall tax payment due by the end of June, leaving the government facing a revenue shortfall of more than 9 billion euros ($9.22 billion), a Treasury document showed on Tuesday.

"It's my intention that they pay it all," Draghi told a news conference. ($1 = 0.9760 euros) (Reporting by Giuseppe Fonte and Angelo Amante; Editing by Keith Weir)