(CNN) -- A decision by world-renowned physicist Stephen Hawking not to attend a conference in Israel in support of an academic boycott of the country has sparked controversy in Israel and a vitriolic debate online.

Hawking, who's a professor at Britain's Cambridge University, had initially accepted an invitation to the high-profile Israeli Presidential Conference, taking place in Jerusalem in June.

His change of heart this week appears to be the result of pressure from Palestinian academics to abide by a boycott set up in protest over Israel's occupation of Palestinian territory.

"A letter was sent on Friday to the Israeli president's office from Stephen Hawking regarding his decision not to attend the Presidential Conference, based on advice from Palestinian academics that he should respect the boycott," a Cambridge University spokesman told CNN on Thursday.

Hawking is also unable currently to fly for health reasons, the spokesman said.

Cambridge University initially said Hawking's poor health was the reason he was no longer attending, according to local media reports. Hawking, who is quadriplegic as a result of an incurable degenerative disease, has had repeated health problems.

Hawking's letter said he had first accepted the invitation "to express my opinion on the prospects for a peace settlement but also because it would allow me to lecture on the West Bank," the conference organizers said.

His decision to boycott the conference, hosted by Israeli President Shimon Peres, a Nobel peace laureate, has prompted a "Twitterstorm."

Some tweeters accuse him of anti-Semitism or comment on his physical disabilities, while others applaud his support for the Palestinian academics.

One tweeter, Ali Abunimah, observes: "Amazing how many Israelis on Facebook want Stephen Hawking dead, electrocuted or made to suffer in other nasty ways."

Haaretz writer Chemi Shalev, who describes himself as a "political junkie, proud father, concerned Israeli, veteran journalist," tweets: "My take: Stephen #Hawking is now the academic boycott movement's unlikely poster boy."

'Outrageous and improper'

Israel Maimon, chairman of the Presidential Conference, said Hawking's decision to pull out of the event was wrong.

"The academic boycott against Israel is in our view outrageous and improper, certainly for someone for whom the spirit of liberty lies at the basis of his human and academic mission," he said in a statement.

"Israel is a democracy in which all individuals are free to express their opinions, whatever they may be. The imposition of a boycott is incompatible with open, democratic dialogue."

Some 5,000 people from around the world are expected to attend, Maimon said, to hear speakers who include global technology company executives, academics, Nobel laureates, artists and past and present world leaders.

Former U.S. President Bill Clinton, Soviet-era President Mikhail Gorbachev and former UK Prime Minister Tony Blair are all expected to attend, he added.

Hawking, who's also a cosmologist, astronomer and mathematician, is the author of books including the best-seller, "A Brief History of Time: From the Big Bang to Black Holes."

The Boycott, Divestment and Sanctions movement was established in 2005 by Palestinian civil society groups, which called for international groups and "people of conscience" to boycott or put pressure on Israel "until it complies with international law and Palestinian rights."

Omar Barghouti, one of the founding members of the movement, told CNN: "Stephen Hawking is the most prominent academic today to respect the Palestinian boycott guidelines and to refuse to visit Israel. This reminds us of the moral weight of academics in the boycott of apartheid of South Africa."

He said Hawking had been convinced by the "unanimous Palestinian voice" he heard from his contacts within the Palestinian community.

"There is deep appreciation among the Palestinians for Professor Hawking's respecting the boycott, and we sincerely hope that we convince many hesitant academics to follow suit and to shoulder a moral responsibility of boycotting Israel until it complies with international law," Barghouti said.

The Jerusalem Post reports that Hawking has visited Israel four times, most recently in 2006, when he lectured at Israeli and Palestinian universities.

West Bank housing

Israel's government gave initial approval Wednesday to plans to build 296 housing units in the settlement of Bethel, near the West Bank city of Ramallah.

Palestinian Authority President Mahmoud Abbas strongly condemned the decision, the official Palestinian news agency WAFA said Thursday.

Presidential spokesman Nabil Abu Rudeina, in a media statement quoted by WAFA, said the Israeli move would sabotage the peace process and efforts made by the U.S. administration to move it forward.

A U.N. Human Rights Council report in January said Israeli settlements had taken a "heavy toll" on the rights and sovereignty of Palestinians.

It outlined the consistent violation of Palestinians' rights in what it called a "creeping annexation" by Israel in East Jerusalem and the West Bank.

Palestinians welcomed the report's findings, but Israel, which considers the Human Right Council to be biased, said the report would hurt the peace process.

There are about 250 settlements in the West Bank and East Jerusalem, the report said, all started since Israel seized the lands after the Six Day War in 1967.

Israel's consistently growing presence in East Jerusalem and the West Bank has caused great tension between Israel and the Arab world, including Palestinians. Israel says its presence is needed for security.

CNN's Kareem Khadder, Stephanie Halasz, Michael Schwartz and Saad Abedine contributed to this report.