NEW YORK -- Senator Lindsey Graham called for a landmark, decade-long defense agreement between Israel and the United States to be renegotiated on Sunday.

The Republican senator from South Carolina said that the memorandum of understanding, worth $38 billion in defense funding to Israel through 2028, offers insufficient missile defense aid at a time when Israel is facing an unprecedented array of missile threats from Iran and its proxies.

"I would ask President Trump and Bibi to sit down and renegotiate this deal," Graham told the annual Jerusalem Post conference in New York, referring to Prime Minister Benjamin Netanyahu by his nickname. "I want to give Israel more for missile defense."

When the MOU originally concluded in 2016, between the Netanyahu government and the Obama administration, Graham rejected caps the deal places on Congress, which appropriates funds to specific Israeli defense needs. The agreement was the first of its kind between Israel and the US to incorporate missile defense aid and ensures Israel receives $500 million a year for those programs.

Per the agreement, Israel will not request additional defense funds from Congress outside emergency circumstances. The MOU is the largest defense agreement the US has ever signed with a foreign nation.

Trump spoke with Netanyahu on Saturday to discuss "the problems posed by the Iranian regime’s destabilizing activities," the White House said. Israel's defense minister also met with his American counterpart as well as Trump's national security adviser in Washington this week.

Their meetings come amid warnings from Liberman that Israel would strike at Tehran itself if Iranian rockets were ever to cross Tel Aviv skies.

"This is a moment of historical significance," Graham said, speaking to the conference of the Iranian threat. If Israel goes to war on its northern border with Iranian forces, "we stand behind them, and we give them whatever we need," he added.

Graham has been a frequent critic of the 2015 Iran nuclear deal brokered under the Obama administration, and has praised Trump for his approach so far to the agreement. The president is threatening to withdraw from the deal by May 12 unless European powers come up with "substantial fixes" to some of its most controversial provisions.

"I want to applaud President Trump for understanding this deal sucks," Graham said. "I hope we get out unless we make it better, because its a lousy deal."

Graham said it was fundamentally mistaken to grant Iran a right to enrich uranium on its own soil as the US tells its Arab Gulf allies they are not allowed to do so.

"It sets up a nuclear arms race," he said. "You're telling your allies you can't enrich and reprocess ... but we're allowing Iran, a mortal enemy of everyone in this room, do it."

The senator saved his criticism of the president for his policy on Syria, where Iran is working to build a permanent military presence, contiguous with its forces in Iraq and its proxies in Lebanon.

"I hope president trump will allow no-fly zones to exist in Syria," Graham said. "This is a very big thing, Mr. President– we can't get this one wrong."