US presidential hopeful Bernie Sanders is the only candidate for the country's top post who has decided to not take part in next week's conference for the pro-Israel lobbying group AIPAC.

In a letter to Robert Cohen, the chief of the American Israel Public Affairs Committee, on Friday - Sanders, the first Jew to ever win a presidential primary in the US, expressed regret that he could not conduct a speech at the event due to his busy campaign schedule.

"Obviously, issues impacting Israel and the Middle East are of utmost importance to me, to our country and to the world," he said.

"Unfortunately, I am going to be travelling throughout the West and the campaign schedule that we have prevents me from attending."

Sander's decision came after more than 18,000 people signed petitions calling for Sanders to turn down AIPAC's invitation to join the conference.

A statement posted on the two petitions, both launched by Max Blumenthal - a prominent activist and author who opposes Israel's occupation of Palestinian territories - said that Sanders "does not belong" in the conference, which it said features "Islamophobes, anti-immigrant activists and religious extremists".

AIPAC, considered the main arm of the pro-Israel lobby in the US, has been accused of promoting discriminatory and harsh policies against Palestinian civilians.

READ MORE: Why Muslim Americans should vote for Bernie Sanders

Meanwhile, Sanders has called for equality between Palestinian and Israeli communities.

"I will make every single effort to bring rational people on both sides together, so that hopefully we can have a level playing field, the United States treating everybody in that region equally," he said.