One of Israel's great living writers, Amos Oz, says people who say Israel should not exist are anti-Semitic.
Speaking in an interview with BBC Newsnight, he said strong criticism of Israel is legitimate, but to argue there should be no Israel "that's where anti-Zionism becomes anti-Semitism".
Oz's books have been published in more than 40 languages.
He is regarded as a liberal and is firmly in favour of a two-state solution for Israel.
In recent months, the Labour Party in the UK has been embroiled in a row over anti-Semitism, and whether the party has a problem on the issue.
Oz told Newsnight's Kirsty Wark: "I can tell you exactly where I draw the line. If people call Israel nasty, I to some degree agree. If people call Israel the devil incarnated, I think they are obsessed - they are mad. But this is still legitimate."
"But if they carry on saying that therefore there should be no Israel, that's where anti-Zionism becomes anti-Semitism, because none of them ever said after Hitler that Germany should cease to exist, or after Stalin that there should be no Russia."
"Saying that Israel should cease to exist, or should not have come into being, this is crossing the line."
Amos Oz has won numerous awards for his books and has also commented widely on political issues. His latest novel, Judas, is a love story set in Jerusalem in 1959-60.
In February 2015, hundreds of UK artists signed a letter announcing they would take part in a cultural boycott of Israel. They said they would not accept professional invitations to Israel, or take any funding from organisations linked to the government.
Other prominent artists - including writer JK Rowling and historian Simon Schama - later criticised the move as "divisive and discriminatory".
Oz told Newsnight he believes cultural boycotts of Israel are counter-productive.
"I think boycott is hurting the wrong people. The idea that all Israelis are villains is a childish idea. Israel is the most deeply divided, argumentative society. You'll never find two Israelis that agree with one another - it's hard to find even one who agrees with himself or herself."
"Boycott is the wrong way because it hardens the Israeli resistance, and it deepens the Israeli paranoia that the whole world is against us."
"Boycott was very effective in the case of South Africa. But you have to be very stupid to think the prescription - the medicine that worked very well against cholera -will also kill the plague.
"This is a kind of laziness - mental laziness. South Africa was bad. The Israeli occupation of Palestinian territories is bad, in a totally different way. You need a different prescription."
Amos Oz was speaking to BBC Newsnight's Kirsty Wark. Watch the full interview on Newsnight at 22:30 on BBC Two, or catch up afterwards on iPlayer