House Democrats have asked secretary of state Marco Rubio to publicly announce that Israel possesses nuclear weapons, arguing that Washington must end decades of ambiguity over the issue amid the conflict with Iran.

In a letter sent on Monday, 30 Democrats wrote that it was unsustainable for Donald Trump to collaborate with Israeli prime minister Benjamin Netanyahu on a military campaign against Iran – with the stated goal of preventing the country from obtaining a nuclear weapon – without publicly acknowledging the US ally’s possession of the bomb.

“We are, in the fullest sense, fighting this war side by side with a country whose potential nuclear weapons program the United States government officially refuses to acknowledge,” reads the letter, which was led by Texas Democrat Joaquin Castro.

“Congress has a constitutional responsibility to be fully informed about the nuclear balance in the Middle East, the risk of escalation by any party to this conflict, and the administration’s planning and contingencies for such scenarios. We do not believe we have received that information.”

Israel has never acknowledged its nuclear weapons programs and no US administration has publicly stated that it exists, despite considerable evidence to the contrary.

The program traces its origins to the 1950s, with assistance from US allies including France and apartheid South Africa. Yet US presidents have for decades avoided discussing the subject, with Barack Obama responding to a reporter’s question about it early in his presidency by saying he did not wish to “speculate”.

The Democrats’ letter notes that other US government officials have essentially admitted its existence. In a 2006 confirmation hearing after George W Bush nominated him as secretary of defense, Robert Gates said of Iran: “They are surrounded by powers with nuclear weapons – Pakistan to their east, the Russians to the north, the Israelis to the west and us in the Persian Gulf.”

The lawmakers also noted that Israeli government officials have nodded towards their possession of the weapons, with heritage minister Amichai Eliyahu saying in 2023 that using a nuclear bomb in Gaza was “one of the possibilities” after the 7 October attacks. In 2006, Ehud Olmert, then Israel’s prime minister, told a German broadcaster that Iran was “aspiring to have nuclear weapons, as America, France, Israel, Russia”.

The Democrats objected to the continued reticence by Trump administration officials to discussed the subject openly, noting that when Castro asked Thomas DiNanno, the under secretary of state for arms control and international security, to detail Israel’s nuclear capabilities at a congressional hearing in March, he responded that he could not answer.

“The United States openly acknowledges the nuclear weapons programs of the United Kingdom, France, India, Pakistan, Russia, China, and North Korea. We ask that Israel be held to the same standard as any other foreign country, and that the United States government speaks candidly about its potential nuclear weapons capabilities, whatever they may be,” the letter reads.

The lawmakers add that the continued ambiguity over Israel’s possession of the weapons harms efforts to transparently address nuclear nonproliferation in the Middle East, noting that Saudi crown prince Mohammed bin Salman has stated that his country would seek to add the bombs to their arsenal if Iran develops their own.

“We ask that you hold Israel to the same standard of transparency that the United States expects from any other country that may be pursuing or retaining nuclear weapons capability,” the lawmakers told Rubio.