The Obama administration has offered to sell $115bn worth of weapons to Saudi Arabia over its eight years in office, more than any previous US administration, according to a new report.

The surge in sales is in part to reassure the Saudi monarchy of US backing in the wake of last year’s nuclear deal with Tehran, which raised fears in the Gulf that Washington would tilt more towards Tehran in its foreign policy.

The report’s author, William Hartung of the Centre for International Policy, said another factor was a drive by US arms manufacturers to boost sales to compensate declining procurement by the Pentagon. However, the most recent deals – such as the offer to sell more than 150 M1A2 Abrams battle tanks for an estimated $1.15bn – were principally intended to replenish the Saudi arsenal, depleted in the war in Yemen.

“I think that though the Obama administration is not thrilled about the Yemen episode; it feels it can’t stay out of it, because of the need to reassure the Saudis,” Hartung said.

His report found that since taking office in January 2009, the Obama administration has offered to sell $115bn in weapons to Saudi Arabia, half of which are accounted for by deals that are still in the pipeline.

“There are $57bn in sales in formal agreements so far, which is also head and shoulders above other administrations,” Hartung said.

The report comes as concerns about the UK’s arms sales to Saudi Arabia and their implication in potential war crimes in Yemen have split MPs on parliament’s arms control committee.

Arms sales over the eight years of the Obama administration have also included combat aircraft, attack helicopters, bombs, air-to-ground missiles, warships and military training. A division of Northrop Grumman is involved in a $4bn train-and-equip programme for the Saudi Arabian national guard, which has reportedly played a key role in the Yemen intervention.

The latest tank deal has drawn resistance from congressional Democrats, who have called for a freeze on arms sales to Saudi Arabia, because of its bombing of civilian targets in Yemen. UN officials have estimated that airstrikes by the Saudi-led coalition are responsible for most of the 3,000 civilian casualties in the war so far, twice as many as those caused by Houthi insurgents and other forces in the conflict put together.

Ted Lieu, a Democratic congresman from California, took a leading role in a letter by 64 members of Congress calling for the tank deal to be delayed, given the coalition’s campaign’s “deeply troubling impact on civilians”.

“I do not oppose assisting the country of Saudi Arabia, which has been a longstanding ally of the United States,” Lieu told the Guardian in a written statement. “What I do fundamentally oppose is continuing to sell arms to a military coalition that has repeatedly committed war crimes. The Saudi-led coalition has killed children, patients, doctors and newlyweds. A significant number of the killings of civilians by the Saudi coalition were nowhere near military targets. I will continue to do all that I can to see that the United States offers no support to Saudi Arabia’s operations in Yemen. The letter that 64 Members of the House sent last week shows that there is a growing chorus in Congress that shares these concerns.”

Tom Porteous, deputy programme director for Human Rights Watch, said: “As Human Rights Watch has documented in frequent field missions to bombing sites, US weapons are being used in coalition attacks that violate the laws of war and in some cases may constitute war crimes … To continue to sell arms is to fuel the flames and enable further violations.”

The US has made appeals to Riyadh to do more to limit civilian casualties, and pointed to Riyadh’s creation of a committee to investigate incidents like the bombing of hospitals as progress in that direction. But the committee has shared information with the UN but not made its findings public. Hartung argued that such messages are least likely to be taken seriously while arms sales are booming.

“I think the US is such a significant supplier of bombs, ammunition, artillery and tanks and playing such an important role in the prosecution of the war in Yemen that there is signficant leverage,” he said. “If the US were to signal that part of that assistance would be frozen or withdrawn if they don’t show they are implementing measures to limit civilian casualties, that would send an effective message. I haven’t seen evidence that they have really made a convincing threat or statement on the consequences for the Saudis if they don’t stop. And any such message would be more powerful if other suppliers like the UK made similar statements.”