Alan Dershowitz has declined a request from Binyamin Netanyahu for the law professor to become Israel's ambassador to the United Nations.

Mr Netanyahu and Foreign Minister Avigdor Lieberman have been searching for an "international media star" to replace the lacklustre Gabriela Shalev, the current ambassador to the UN.

"Netanyahu, who was himself an ambassador to the UN, sees that job as Israel's premier spokesperson abroad," said a senior official at the Foreign Ministry. "That's why he is not interested in appointing a diplomat, but a media performer."

Prof Dershowitz, who was catapulted to fame in the US as defence counsel in a number of high-profile court cases, has become one of Israel's most vocal advocates. His book The Case for Israel is required reading for Israeli diplomats about to go on a foreign posting.

Mr Netanyahu offered him the UN post a few weeks ago and tried again to convince him at a private dinner at the PM's residence in Jerusalem.

If he had accepted, Prof Dershowitz would immediately have received Israeli citizenship, as did Stanley Fischer when he became governor of the Bank of Israel five years ago.

According to his advisers, Mr Netanyahu wanted "a rerun" of the successful Fischer appointment, widely seen as a key move which enabled Israel to ride the storm of the global financial crisis relatively unscathed. But it seems that citizenship was the main reason that Prof Dershowitz declined the job offer.

"I was afraid that it would cause me a problem of dual loyalty which is a difficult situation for an American Jew," he said in an interview last week.

"Since I have been an American patriot all my life, it was hard for me to accept. Israel and the US are allies, but if problems arise, say over Iran, which side would I choose? I always choose the right side: it might not be Israel's."

But Prof Dershowitz promised to continue being "Israel's attorney".