"The purpose of this decision is to support the judicial cooperation between Switzerland and these two states," a government statement read.
In contrast, the Swiss said they were lifting a 2011 block on an initial USD 700 million (590 million euros) worth of assets in Egypt.
That sum has dwindled by around half after Egyptian judicial agreements to "drop criminal proceedings in the most prominent cases with possible links to assets frozen in Switzerland".
In early 2011, Bern's Federal Council said it was freezing the assets of Ben Ali and his entourage as well as of former Egyptian President Hosni Mubarak in the wake of the Arab Spring sweeping the region.
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A similar block followed when conflict-hit Ukraine in February 2014.
In July 2016, the Swiss passed a federal act governs the duration and extension of such measures.
The Tunisian freeze covers 56 million Swiss francs (USD 57 million; 48 million euros) and 70 million francs of Ukrainian assets.
"During the years since these freezes entered into force, several proceedings have been initiated against the main individuals concerned, and the authorities of these countries have taken steps to advance these cases at the judicial level," the Swiss statement said.
It added that it had still to determine the assets' origins were illicit, hence the extension in the hope that "tangible progress" would be made to allow their ultimate repatriation.
In the case of the remaining Egyptian assets, they are still impounded as "despite the joint efforts undertaken, the cooperation between the two countries has failed to produce the anticipated results," Bern said.