US Democratic presidential candidate Bernie Sanders has refused to sign a letter urging President Barack Obama to quickly reach an agreement on a new military aid package for Israel worth more than the current $3 billion per year.

Eighty-three of the 100 senators signed the letter, led by Republican Lindsey Graham and Democrat Chris Coons. Senator Ted Cruz, a 2016 presidential candidate, was one of the 51 Republican signatories.

The letter was signed by 51 Republican and 32 Democratic senators. However, Sanders, an Independent senator from Vermont, was among the 17 senators who didn’t sign the letter.

“It is encouraging to see such strong support for Israel from both parties and the American people,” an Israeli official said.

Washington and Tel Aviv are negotiating a new 10-year US military aid package to replace the $3 billion-a-year agreement that expires in 2018.

Israel last year requested $5 billion in future annual aid but its officials have since lowered their expectation to around $4.5 billion. However, US officials have given lower target figures of around $3.7 billion.

The dispute prompted Israeli officials to suggest last month that Prime Minister Benjamin Netanyahu, in hope of better terms, may await Obama's successor to conclude the deal.

Sanders, who is Jewish, has called for a more “balanced” US Middle East policy, describing Israel’s war in the Gaza Strip in 2014 as “disproportionate.”

“I think that we will not succeed to ever bring peace into that region unless we also treat the Palestinians with dignity and respect, and that is my view,” he said in an interview with CNN that aired earlier this month.

Sanders was the only presidential candidate to skip the annual policy conference of the American Israel Public Affairs Committee (AIPAC), the most powerful pro-Israel lobbying group in Washington, last month.

The Vermont senator has also criticized Israel’s expansion of illegal settlements in the occupied West Bank and called for an end to the siege on Gaza, which has created a dire economic situation in the enclave.