By the end of 2016, the Afghanistan Air Force is due to have 86 Russian-made Mi-17 helicopters. Most of them will have been purchased by the United States from Rosoboronexport, the same state weapons exporter that continues to arm the Syrian government of President Bashar Assad.

Congress is not pleased — but has struggled to do anything about it.

The Pentagon says there is no better, cheaper helicopter than the Mi-17 to operate in Afghanistan’s desert expanses and high altitudes, and that it is the aircraft the Afghans know best.

For its latest order of 30 helicopters, the Defense Department sidestepped a congressional ban imposed last year on using fiscal 2013 funds to buy anything from Rosoboronexport. Instead, the military found the money in its 2012 Afghanistan budget to finance the nearly $600 million contract.

Adding insult to perceived injury, the Pentagon said it would have gone ahead with the contract even if it had to use 2013 funds, under a waiver provision in the ban that allows it to take action it determines to be in U.S. national security interests.

“Gosh sakes, we won the vote 407 to 5,” fumed Rep. James Moran, who spearheaded the prohibition in the House. “These guys are only focused on Afghanistan, and couldn’t care less what is happening in Syria.” Last month, the House Appropriations Committee added a similar amendment to the 2014 defense funding bill.

Sen. John Cornyn, who organized last year’s unanimous Senate vote, chastised the administration for “arrogant circumvention” of bipartisan congressional will and said, “American taxpayers should not be indirectly subsidizing the murder of Syrian civilians.”

The Obama administration lifted sanctions against the company in 2010 as part of its policy “reset” toward Russia, after Moscow suspended delivery of S-300 missiles to Iran — the same advanced antiaircraft system that Rosoboronexport has contracted to provide Assad — and agreed to support U.N. sanctions against Iran.

Pentagon officials said the Mi-17s are the most sensible solution for Afghanistan. “They’ve been using it for years,” Defense Secretary Chuck Hagel said in House testimony in April.

Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, told lawmakers that the purchase was a crucial component of U.S. withdrawal plans from Afghanistan. “We are trying . . . to provide them as much capability as possible so that they can in fact take responsibility for security” when U.S. combat forces leave at the end of 2014, he said.