A black pall of smoke rises above the city following airstrikes allegedly carried out by the Saudi-led alliance targeting a Houthi-held army base in Sana'a, Yemen, 20 August 2015. (Yahya Arhab/EPA)

Coalition airstrikes led by Saudi Arabia reportedly killed more than 65 civilians in the southwestern Yemeni city of Taiz on Friday, as aid officials excoriated the US government for its role in supporting the Arab force that has targeted Houthi rebels since late March.

Salah Dongu'du, project coordinator at Medecins Sans Frontieres (MSF) in Taiz, said in a statement that the strikes hit 17 homes and left at least 37 women and children dead.

"Patients and MSF staff are unable to reach hospitals due to heavy fighting and airstrikes in Taiz," said Dongu'du. "It is very frustrating that people are dying in the streets of Taiz and our teams are unable to reach injured people."

The reported casualties come after Amnesty International said on Tuesday that both sides in the conflict might have committed war crimes. On Wednesday, UN humanitarian chief Stephen O'Brien told the Security Council that coalition bombardment of the Red Sea port in Hodeida were in "clear contravention of international humanitarian law, and are unacceptable."

Also on Wednesday, Human Rights Watch, Amnesty International, and 21 other human rights organizations called on the UN Human Rights Council to establish a commission of inquiry to investigate "serious laws-of-war-violations by all parties in Yemen since September 2014," similar to the one created in the aftermath of last year's war in Gaza.

The Human Rights Council has not responded to the request. Both Saudi Arabia and the United States sit on the Council.

O'Brien also cited the Saudis for failing to pay the $274 million it promised the UN in April for aid operations in Yemen. UN officials say privately that they are growing increasingly frustrated with the Saudi government, which has insisted the donation be routed through a special center established in Riyadh.

More than 21 million Yemenis are in need of humanitarian assistance; UN officials say a coalition blockade of the country has cut off the supply of basic necessities.

In a statement released Friday on Twitter, the White House's National Security Council said it was "deeply concerned" by the August 18 attack "on key infrastructure at Hodeidah port in Yemen," calling the port a "lifeline for medicine, food & fuel to Yemenis."

The Council called for both sides to "resume dialogue for (a) political resolution to the crisis," but stopped short of calling for a ceasefire. Earlier attempts at brokering humanitarian pauses have been completely ignored by both the Houthis and the coalition.

Even as it called attention to the August 18 attack on Hodeida, the US continues to provide logistical support to the Saudi-led coalition, including the very targeting assistance that may be used in such airstrikes like those which hit the port.

"While US forces are not taking direct military action in Yemen in support of this effort, we have, at the request of the GCC [Gulf Cooperation Council], established a joint Combined Planning Cell (JCPC) with Saudi Arabia," a spokesperson for US Central Command told VICE News.

"The JCPC facilitates logistical support, intelligence support and intelligence sharing, targeting assistance, and advisory support," said the spokesperson.

In response to a question about a July 24 strike in Mokha that killed at least 65 civilians, a Pentagon spokesperson said "for operational security reasons," the US could not comment on specific attacks.

Last month, the State Department approved two military sales to the Saudi Kingdom, one a deal for Patriot Missile systems worth an estimated $5.4 billion, and a smaller package of $500 million worth of ammunition for the Royal Saudi Land Forces. In a statement, the State Department said the second proposed deal "will resupply the Royal Saudi Land Forces (RSLF) with the munitions it needs to continue to protect Saudi Arabia's southern border from ongoing attacks by hostile Houthi militia and al Qaeda in the Arabian Peninsula forces."

While US arms sales to their longtime ally are nothing new, the American role in Saudi attacks in Yemen — still largely obscured — has raised questions from human rights officials.

"You'd get the sense from its public statements that the White House views the humanitarian crisis as some naturally occurring phenomenon beyond its control," Scott Paul, Oxfam America's senior humanitarian policy advisor, told VICE News. "To put it bluntly, people are suffering because of a conflict that is supported by the US government in action, if not in rhetoric."

"If the US is serious about putting an end to Yemen's suffering, it will call for an immediate ceasefire and withdraw its support from the coalition, which is preventing aid and commercial supplies from reaching huge segments of the Yemeni population," said Paul.

From the start of the bombardment, advocates have questioned the legal implications of American support for a force that may be committing war crimes.

"By providing logistical and intelligence assistance to coalition forces, the United States may have become a party to the conflict, creating obligations under the laws of war," said Human Rights Watch in an April statement.

At that time, some 311 civilians had been killed by all sides since airstrikes began on March 26. Today, the toll stands at nearly 2,000, according to UN figures. Some 1,000 children have either been killed or wounded.

On Friday, UN spokesperson Eri Kaneko told reporters that "indiscriminant bombing of civilian areas is a violation of international law, and we would encourage an investigation if that were the case."

Houthi rebels and their allies have also been implicated in gross human rights violations. Hundreds of civilians have been killed by the group's indiscriminate shelling in several cities, including Aden and Taiz.

Last week, a senior UN diplomat involved in Yemen negotiations told VICE News that Houthi representatives had conveyed a willingness to withdraw from several cities, including Taiz. On Friday, Kaneko said the Secretary General's envoy for Yemen, Ould Cheikh Ahmed, would travel to Riyadh, where he would convey proposals from Houthis and the General People's Congress, the political party of former President Ali Abdullah Saleh, who has supported the rebels.