It's been called the forgotten war – a punishing campaign of airstrikes by a Saudi Arabia-led coalition that over the last 18 months has destroyed schools and homes, hospitals and crowded marketplaces in Yemen, the Arab world's poorest nation.
Now a single devastating attack that left at least 140 mourners dead at a funeral hall in Yemen's capital, Sana, may push the Obama administration to reconsider its support of the air war spearheaded by Riyadh, and could spark a reappraisal of Western arms sales to Saudi Arabia.
Saudi Arabia has announced an inquiry into Saturday's grisly bombardment of the crowded funeral hall, which was widely blamed on the coalition, although the Saudis have not accepted responsibility. And the Obama administration said it was reviewing its role in the coalition in light of Saturday's attack and a string of similar incidents.
On Monday, the United Nations' human rights chief, Zeid Raad Hussein, cited a "climate of impunity" surrounding the air war, which has killed at least 4,125 civilians by U.N. estimates and benefited the extremists of Al Qaeda and Islamic State.
The campaign of airstrikes began six months after Houthi rebels surged out of their northern strongholds and seized Sana in September 2014, putting the internationally recognized president, Abdu Rabu Mansour Hadi, under house arrest. He subsequently retreated to the southern port city of Aden and later took shelter in Riyadh, the Saudi capital, before returning to Aden.
But the Yemen conflict is essentially a proxy fight, replete with bitter sectarian overtones, between the two powerhouses of the Persian Gulf region – Sunni Muslim Saudi Arabia, which supports Hadi, and Shiite Iran, which backs the Houthis but denies arming them.
Because of Yemen's strategic location alongside key oil-shipping lanes, fighting there has spurred worries about a potential widening of the war. On Sunday, suspected Houthi forces fired a pair of missiles toward the Mason, a U.S. guided-missile destroyer sailing in international waters off the Yemeni coast.
The Pentagon said the projectiles fell harmlessly into the water, causing no injuries or damage, but the episode heightened concerns about security of shipping in the Bab al Mandab, a narrow strait through which millions of barrels of oil pass weekly. Last week, a vessel from the United Arab Emirates came under fire from Yemen near the crucial waterway.
Even before Saturday's bombing, the growing civilian toll in Yemen had galvanized opposition in the U.S. and Britain to lucrative Saudi arms deals. But the Senate last month voted down a bipartisan measure to block a $1.5-billion sale of weaponry to the Saudis.
"This bombing campaign would not be possible without U.S. targeting, U.S. bombs, U.S. refueling," Sen. Chris Murphy (D-Conn.), said in a recent interview. "We are full and total participants in this bombing campaign, and it seems ludicrous to try to absolve ourselves from these casualties."
In Sana, thousands marched Sunday to protest the funeral hall airstrike, one of the war's single deadliest episodes. Rescuers described a scene of unremitting carnage, with a welter of charred bodies and body parts. The U.N., which provided the death toll, also said more than 500 people were hurt.
Angry protesters who took to the streets of the capital blamed not only the Saudi-led coalition, but also the U.N., for failing to stem the bloodshed, and the United States, Riyadh's ally, which has provided logistical and intelligence support for the air campaign.
That support was reportedly scaled back over the summer, amid a rising outcry over civilian casualties in Yemen, when some U.S. military personnel were diverted from a task force aiding the coalition.
But the Saudis have previously weathered international denunciations over the conduct of the air war, including a wave of opprobrium in August after a deadly airstrike on a hospital in the Houthi-held northern province of Hajjah that was supported by the Paris-based Doctors Without Borders.
The attack, which killed at least 19 people, was the fourth such strike on a medical facility backed by the group. In response, Doctors Without Borders pulled its staff out of six hospitals in the north, citing "indiscriminate" bombardment.
Human rights groups, which have exhaustively documented strikes on medical facilities, residential areas and civilian targets such as a potato-chip factory, renewed calls for an end to the air campaign after Saturday's attack — even while voicing frustration that previous appeals have gone unheeded.
International concern was mounting, however. Germany's foreign minister, Frank-Walter Steinmeier, on Monday called the funeral hall strike a "cruel act" that threatened to pull in other regional actors. Iran, which has denied arming the Houthi rebels, denounced the Saudi-led air campaign as "tragic and horrific" and sought U.N. intercession for Iran to send in humanitarian supplies and airlift wounded victims out.
In Washington, there were growing signs of the conflict's unpopularity. On Sunday, citing a series of attacks that have killed or maimed civilians, National Security Council spokesman Ned Price said American cooperation with the Saudi-led coalition was "not a blank check."
Aside from the bombardment's direct toll, civilian suffering has intensified in recent months, after the breakdown of U.N.-brokered talks over the summer in Kuwait. A cholera outbreak is raging in Sana, UNICEF reported last week, and food and medical supplies are scarce. Parents in Sana take to social media to describe their children's terror at the nightly roar of airstrikes.
In Yemen's complex tribal society, Saturday's attack also had what may be lasting political repercussions. The hundreds of mourners at the funeral hall included dozens of influential tribal leaders who were there to pay tribute to the late patriarch of a powerful clan.
Saudi Arabia, which has often responded dismissively to past criticism of the air campaign, conveyed "deep regret" over the bombing in a letter to the U.N. Security Council and sought to strike a conciliatory note over the funeral hall attack, promising transparency in the investigation it says it has launched.
The kingdom is already the target of concerted criticism over its human rights record. The U.N. has called on Saudi Arabia to repeal laws allowing punishments including stoning, amputation and flogging, and groups including Human Rights Watch have demanded that Saudi Arabia be suspended from the U.N.'s Geneva-based Human Rights Council.
The kingdom has aggressively worked to counter formal expressions of international condemnation, such as attempts to place the Saudi-led coalition on a list of violators of children's rights, and has largely prevailed. But the political climate surrounding the Yemen conflict may be changing.
U.N. Secretary-General Ban Ki-moon, who issued a strongly worded statement Sunday condemning the funeral hall bombing, suggested that the world body might yet seek to hold Saudi officials accountable for the ever-rising tide of destruction and death in Yemen.
"Those responsible," he said, "must be brought to justice."