The Swiss government says it has identified potential assets to be frozen worth 830m Swiss francs (nearly $1bn or £600m) belonging to Libyan leader Muammar Gaddafi and the ousted presidents of Egypt and Tunisia.

Swiss president and foreign minister Micheline Calmy-Rey, speaking in the Tunisian capital, Tunis, said the assets include 360m Swiss francs that may belong to Gaddafi or his entourage.

She said Switzerland had also linked 410m Swiss francs to the former Egyptian president, Hosni Mubarak, and 60m Swiss francs to Tunisia's deposed autocrat, Zine El Abidine Ben Ali.

Switzerland has ordered banks and other financial institutions to freeze possible assets belonging to the three men and their key supporters to prevent the funds from being secretly withdrawn. The Swiss government has said Tunisia and Egypt have already started legal proceedings to claim the assets.

The government added that neither country has yet provided the necessary evidence of possible criminal wrongdoing involving the money.

Switzerland froze assets linked to Ben Ali and 40 people in his entourage on 19 January, less than a week after he was toppled by popular revolt. On 11 February, Switzerland froze assets of Mubarak and his associates.

The Swiss government sent diplomatic cables to Tunisia and Egypt in late March explaining they must submit evidence so authorities can decide if the offences are punishable in Switzerland. In both cases, the money will remain locked away for three years while the two countries satisfy Swiss legal requirements.

The Swiss also have asked a court to authorise the seizure of millions of dollars frozen in accounts belonging to former Haitian dictator Jean-Claude "Baby Doc" Duvalier.

The Swiss finance department said it has initiated proceedings before the federal administrative court, a quarter-century after the funds were first frozen in Switzerland. That was shortly after Duvalier's removal from power in 1986.

Earlier this year, Switzerland also froze funds tied to Laurent Gbabgo, the former president of Ivory Coast who refused to cede power and finally was captured.

Switzerland is trying hard to shed its reputation as a favoured location for dictators' money because of its banking secrecy rules, and has established an investigative unit to help track down hidden funds.

The three-year freeze on assets is the norm, which Calmy-Rey and the other six members of Switzerland's governing federal council have said is meant to give nations time to draft possible criminal cases against former leaders.

Calmy-Rey says Switzerland is willing to help make those cases because it wants to avoid being used to hide funds illegally. A new law affecting the seizure of assets went into effect on 1 February that makes it easier for the Swiss government to freeze and seize the money.