Days before Prime Minister Benjamin Netanyahu is set to give a contentious speech before a joint session of Congress on the dangers of a bad nuclear deal with Iran, the Obama administration went on the offensive Friday charging that while the Israeli leader was vehemently opposed to the emerging agreement, he had failed to present an alternative.

Senior administration officials told reporters during a briefing Friday that an imperfect deal with Iran to curb its nuclear program by freezing its efforts for a time was preferable to a breakdown in talks which could see Iran race for the bomb, according to the New York Times.

The officials were talking days ahead of the controversial visit to Washington by Netanyahu, who is due to address the US Congress on Tuesday on why he believes the looming Iran deal is a bad move, despite opposition from the White House which sees the trip as interference with the talks and as inappropriate ahead of Israel’s elections later in March.

“The alternative to not having a deal is losing inspections, and an Iran ever close to having the fissile material to manufacture a weapon,” a US official told the paper.

But concerns over the proposed deal, the paper reported, include the fear that it provides an ability for Iran to resume its efforts in the last years of a phased agreement and to be closer to the bomb than it is now in those years — two or three months rather than a required year, which is one of the US’s demands in the first stage of the agreement.

Officials were also unclear about when and how Iran would have to respond to questions by the IAEA about its nuclear program.

The US on Friday set out what it called its “bottom lines” to reach a deal, ahead of new talks next week which are reported to be progressing.

“We have made a substantial amount of progress. Ultimately, Iran has to make a very significant political decision to allow the flexibility to close this deal,” the official told the NYTimes.

US Secretary of State John Kerry is headed back this weekend to Switzerland, where he will meet once again with his Iranian counterpart Mohammad Javad Zarif.

A March 31 deadline for a political framework for the deal is looming with negotiators saying they will aim to pin down the final technical details by June 30.

Staking out the broad outlines of a deal Friday — without going into specifics — another US official spelled out where Washington was standing firm:

— Iran should not be allowed to develop weapons-grade plutonium at its Arak reactor. “We’re discussing how Iran can convert that Arak reactor to serve a different purpose,” the official said.

— Iran should not use its Fordo nuclear plant to enrich uranium; that would leave only Iran’s Natanz plant capable of enriching uranium, which at high grades can be used in nuclear weapons.

— Any deal must ensure that it would take Iran a year to gather enough fissile material to make a bomb.

— Iran would “reduce significantly” its current number of operating centrifuges and its domestic stockpile.

— Iran must agree to unprecedented inspections of both nuclear and production facilities as well as uranium mines and mills, and suspect sites.

— The US is pursuing a deal in which relief from international sanctions demanded by Iran “is phased in over a period of time.”

“We are insisting on the principle that sanctions can snap back into place if Iran were to violate the agreement,” the US official said.