Twenty Democratic US senators, on Wednesday, expressed support for a potential Israeli-Saudi normalisation deal but laid out concerns about any US security guarantees or nuclear assistance to Riyadh, Reuters reports.

In a letter to President Joe Biden, the senators underscored resistance the White House could face from Congress if the administration brokers a landmark agreement opening diplomatic ties between long-time foes Israel and Saudi Arabia in return for Washington meeting Riyadh’s demands.

Negotiations have been advancing, but US officials caution that much work remains.

Among the suggestions of Biden’s fellow Democrats is that any agreement includes “meaningful” provisions to preserve the option of a two-state solution to the Israeli-Palestinian conflict. Israel’s far-right government is expected to resist any big concessions to the Palestinians.

“Peace between Israel and its neighbours has been a long-standing goal of US foreign policy, and we are maintaining an open mind about any agreement that would potentially deepen the political, cultural and economic ties between Saudi Arabia and Israel,” the senators wrote.

But they cited misgivings about what the Saudis want.

READ: Israel growing frustrated with US over normalisation with Saudi Arabia

Saudi Arabia is determined to secure a military pact requiring the United States to defend the Kingdom in return for opening ties with Israel and will not hold up a deal even if Israel does not offer major concessions to Palestinians in their bid for statehood, three regional sources familiar with the talks have told Reuters.

A high degree of proof would be required to show that a binding defence treaty with Saudi Arabia – an authoritarian regime which regularly undermines US interests in the region, has a deeply concerning human rights record, and has pursued an aggressive and reckless foreign policy agenda – aligns with US interests

the letter stated.

Both Democrats and Republicans have previously denounced Riyadh for intervention in Yemen, moves to prop up oil prices and its role in the 2018 killing of journalist, Jamal Khashoggi.

The letter also stated concerns about the Saudis’ request for civilian nuclear help and access to advanced weaponry.

It said the US must hold the Saudis to the “gold standard” of Section 123 of the US Atomic Energy Act, establishing a framework for peaceful nuclear cooperation.

The White House did not immediately respond to a request for comment.

Senators leading the letter effort included Middle East sub-committee Chair, Chris Murphy, No. 2 Democrat Dick Durbin, Chris Van Hollen and Peter Welch.

READ: Netanyahu says Iran will not prevent Israel from normalising relations with Saudi Arabia