The Foreign Ministry is furious over news that Mahmoud al-Zahar, a senior Hamas official based in the Gaza Strip, recently headed a Hamas delegation to Switzerland for talks with Swiss diplomats.
A senior Foreign Ministry official said the visit will further destabilize already shaky relations between Jerusalem and Bern, after Iranian President Mahmoud Ahmadinejad visited Switzerland in April for the "Durban 2" United Nations anti-racism conference.
China's news agency broke the story of Zahar's visit nearly two weeks ago.
Officials at the Israeli Embassy in Bern were surprised by the report, since they knew nothing about the June visit.
The embassy has requested clarifications from the Federal Department of Foreign Affairs, but Israeli officials say the responses have not been satisfactory.
One Jerusalem officials said it was many days before the Swiss confirmed the Hamas visit to the embassy.
Swiss officials told Israel's ambassador in Bern, Ilan Elgar, that the Hamas delegation was invited to Geneva by a nongovernmental research institute.
The Foreign Ministry source, however, noted that Swiss diplomats, including the Swiss envoy to the Middle East, met with the delegation during a conference at the institute.
When Elgar requested official clarification regarding the visa issued to the delegation, he was told by the Swiss foreign ministry, "In Switzerland, Hamas is not considered a terrorist organization."
Tensions between Jerusalem and Bern began to build about a year and a half ago, when the Swiss foreign minister went to Iran to sign a major gas purchase contract.
In May, in the wake of Ahmadinejad's visit to Geneva and the official working meeting with him held by Swiss President Hans-Rudolf Merz, Israel recalled Elgar to Jerusalem for consultations in protest.