Switzerland's top negotiator in talks to resolve disputes over tax evasion with Europe and the U.S. is stepping down.

The Finance Ministry said Friday that Michael Ambuehl will leave his post at the end of August and go into academia.

The move comes at a crucial time for Switzerland, which is trying to reach a deal with the U.S. to save Swiss banks and their employees from prosecution for aiding U.S. tax cheats.

During Ambuehl's three-year tenure, Switzerland sealed tax deals with Britain and Austria. A deal with neighboring Germany was blocked by that country's Parliament.

Previously Ambuehl was Bern's top negotiator on Iran, where Switzerland represents U.S. interests.

According to a ministry statement Ambuehl's boss, Finance Minister Eveline Widmer-Schlumpf, "took note of this decision with regret."