The White House is calling for the United Nations to examine Iran's role in the conflict in Yemen, alleging the Iranian government is perpetuating the fighting in order to "advance its regional ambitions."
U.S. ally Saudi Arabia accused Iran of supplying Houthi rebels with arms, including a missile the Saudis intercepted after it was fired at an airport in Riyadh.
Saudi Arabia leads a coalition battling the Houthis in support of Yemen's internationally recognized government, and said earlier this week Iran's actions could be considered "an act of war."
A White House statement Wednesday expressed support for Saudi Arabia and other allies in the region and said Iran has violated U.N. prohibitions on arms transfers.
"Houthi missile attacks against Saudi Arabia, enabled by Iran's Islamic Revolutionary Guard Corps, threaten regional security and undermine U.N. efforts to negotiate an end to the conflict," the statement said.
Iran has supported the Houthis, but denies arming them.
Iranian Foreign Minister Mohammad Javad Zarif criticized Saudi Arabia for its role in the Yemen conflict in a series of Twitter posts Tuesday.
"[Saudi Arabia] bombs Yemen to smithereens, killing 1000's of innocents including babies, spreads cholera and famine, but of course blames Iran," Zarif wrote. "[Saudi Arabia] is engaged in wars of aggression, regional bullying, destabilizing behavior and risky provocations. It blames Iran for the consequences."
The Saudi-led coalition began an intensive campaign of air strikes against the Houthi rebels in March 2015. Since then, the United Nations reports more than 14,000 civilian casualties. These include nearly 5,300 people killed and almost 8,900 injured.
The United Nations adds the actual number of civilian deaths and injuries is likely to be far higher, and the conflict has created a humanitarian emergency for millions of people.
Saudi Arabia responded to the missile firing Saturday by announcing a temporary air, land and sea blockade.
The United Nations said Tuesday that move blocked all humanitarian operations in Yemen and called for Saudi Arabia to immediately reverse the ban.