Saudi-led airstrikes against Shiite Houthi rebels in Yemen continued on Thursday as Iran called the two-week campaign a “genocide.”

Iran is accused of providing military support to the Houthi rebels, pitting the Shiite powerhouse against the Saudi-led Sunni coalition bombing Yemen.

The Saudi-led campaign is backed by increasing U.S. arms shipments and intelligence sharing.

Saudi Arabia argues that the Houthis are an Iranian proxy force. The Saudi-led Sunni Gulf countries that have formed a coalition accuse Iran of arming the Houthis, but Iran and the rebels deny those allegations.

The U.S. is also contradicting the Iranian denials about providing military support to the Houthis.

In an interview Wednesday night with “PBS NewsHour,” Secretary of State John Kerry said that Washington knew Iran had been providing military supplies to the Houthis in Yemen, warning that the United States “is not going to stand by while the region is destabilized.”

“We’re very concerned about what’s going on there, and it’s just not a fact. They have been,” said Kerry when asked about Iran denying that it is lending support to the Houthis.

“There are obviously supplies that have been coming from Iran. There are a number of flights every single week that have been flying in and we trace those flights and we know those. We’re well aware of the support that Iran has been giving to Yemen,” he continued. “And Iran needs to recognize that the United States is not going to stand by while the region is destabilized, or while people engage, you know, in overt warfare across the lines, international boundaries and other countries.”

Kerry made those comments after a senior U.S. diplomat said the U.S. was speeding up arms shipments and enhancing intelligence sharing with the Saudi-led alliance.

“Saudi Arabia is sending a strong message to the Houthis and their allies that they cannot overrun Yemen by force,” U.S. Deputy Secretary of State Antony Blinken told reporters in the Saudi capital Riyadh on Tuesday, Reuters reports.

“As part of that effort, we have expedited weapons deliveries, we have increased our intelligence sharing, and we have established a joint coordination planning cell in the Saudi operation center,” he added.

Meanwhile, Iran’s Supreme Leader Ayatollah Ali Khamenei condemned the Saudi-led airstrikes, saying, “This is a crime, genocide and legally pursuable,” and warning that “the Saudis will lose” and that “Yemenis will resist and will win,” reports The Associated Press.

On Thursday, Iranian President Hassan Rouhani reportedly called for a cease-fire in Yemen to allow for negotiations on resolving the conflict.

“To the countries in the region, I say, let’s adopt the spirit of brotherhood, let’s respect each other and other nations. A nation does not give in through bombing,” said Rouhani. “Do not kill innocent children. Let’s think about an end to the war, about cease-fire and humanitarian assistance to the suffering people of Yemen.”

The Houthis have joined forces with military units loyal to former Yemeni President Ali Abdullah Saleh and together they have seized 10 of Yemen’s 21 provinces.

On the ground, Houthi forces and their allies are fighting against local armed groups loyal to the internationally recognized Yemeni President Abd-Rabbu Mansour Hadi.

The Houthis and their allies are reportedly making gains. They overran Ataq, capital of the oil-rich southeastern Shabwa province and made advances in the southern port city of Aden where intense fighting continues.

The World Health Organization on Wednesday said that at least 643 civilians and combatants have been killed and more than 2,200 have been injured in Yemen since March 19.

CNN reports that the Saudi-led strikes are taking a heavy toll on civilians.

In a statement on Monday, the United Nations International Children’s Emergency Fund (UNICEF) said that at least 74 children have been killed and another 44 maimed since the Saudi-led coalition began launching airstrikes against suspected Houthi targets in Yemen about two weeks ago.

Those figures were released hours before Yemeni officials said the Saudi strikes hit a school in Ibb province, killing at least three students and reportedly wounding at least a half a dozen more.

The conflict in Yemen is reportedly providing the powerful al-Qaeda in the Arabian Peninsula (AQAP) with an opportunity to gain new territory. AQAP’s most ardent opponents on the ground are the Houthi rebels and their allies.

Follow Edwin Mora on Twitter: @EdwinMora83.