CAIRO (Reuters) - The sons of Egypt's ousted President Hosni Mubarak own assets worth $340 million in Switzerland and might have been involved in money laundering, a justice official tasked with recouping ill-gotten gains from abroad said on Monday.

Mubarak, toppled in a popular uprising in February, and his sons Gamal and Alaa are on trial for corruption and abuse of power. European governments agreed after Mubarak was ousted to freeze his assets and those of 18 associates.

Egyptians who took part in the uprising in which at least 850 people were killed are anxious to see Mubarak and his allies punished for abuses during his three-decade rule.

"The committee has obtained information that confirms that Mubarak's sons have deposits in Swiss banks worth $340 million, of which Alaa owns $300 million," Assem el-Gohari, head of the Illicit Gains Authority, said in a statement.

He said Switzerland had frozen Mubarak family assets worth $450 million and that Swiss authorities were investigating accusations of money laundering by Alaa Mubarak and two other former regime figures.

Gohari said Mubarak's closest aide Hussein Salem and his family own assets worth $4 billion in various countries which they switched into cash and deposited in banks in Hong Kong, the United Arab Emirates and other countries.

Salem, his son and daughter were last week sentenced in absentia to seven years in jail and a combined fine of more than $4 billion for money laundering and profiteering.

Spanish authorities have frozen millions of euros (dollars) in bank accounts as well as property and luxury vehicles linked to Salem, who is under house arrest since June on accusations of money-laundering, which were brought in Spain and are separate from Egyptian charges.

"The committee has its hands on a lot of information and documents regarding the fortunes of the previous regime's figures but the time to announce them hasn't come yet, so as to preserve secrecy and not lose what we have achieved," Gohari said.

(Reporting By Tamim Elyan)