The Obama administration has moved to block sales of cluster bombs to Saudi Arabia for use in Yemen, amid reports of mounting civilian casualties there, a US media report said Saturday.

The report in the journal Foreign Policy, citing US officials, said that the White House had quietly placed a hold on the transfer of such munitions to the Sunni kingdom as it carries out a bloody war on Shiite rebels in Yemen.

A Saudi-led coalition has been fighting the Iranian-backed Huthis since March 2015, trying to roll back their control of wide swaths of Yemen.

Asked by AFP for comment, an administration official said that "we are aware of reports that the Saudi-led coalition used cluster munitions in the armed conflict in Yemen, including in areas in which civilians are alleged to have been present."

"We take such concerns seriously and are seeking additional information," the official added.

Foreign Policy said it was the first concrete display of unease by US officials over bombings that human rights activists say have killed and injured hundreds of civilians, including children.

Cluster bombs are designed to kill enemy personnel and destroy vehicles or runways.

But because they disperse scores of tiny bomblets over a wide area -- some of which may not explode for years or even decades after being dropped -- they pose a particular threat to civilians.

They were banned by an international treaty in 2008, but Russia and the United States, both major suppliers, failed to sign it.

The US antiwar group CodePink on Sunday applauded the administration decision, and called on President Barack Obama to suspend all arms transfers to the kingdom.

Amnesty International said Monday that the Saudi use of cluster bombs had created "minefields" for civilians in Yemen. It has called, along with Human Rights Watch, for a ban on arms sales to the Saudis.

The United States has sold the Saudis millions of dollars' worth of cluster bombs and provided other forms of military support.

The reported move on cluster bombs comes amid growing criticism by American lawmakers of the Saudi monarchy. Legislators are unhappy that the Saudis have not done more to fight the militants of the Islamic State group in Syria, Yemen and elsewhere.

The longstanding US-Saudi relationship, built on an exchange of American security backing for a reliable supply of Saudi oil, has been strained as the United States has gained greater energy independence even while reaching historic agreement with the Saudis' bitter regional foe Iran.