The White House on Monday vowed a "very consequential response" to a drone attack on a base in Jordan that killed three American troops, with President Joe Biden blaming Iran-backed militants.

The casualties -- the first US military deaths in an attack in the region since the Israel-Hamas war began -- raised fears of an escalating conflict, as fighting rages in Gaza.

Washington's response will be "very consequential," National Security Council spokesman John Kirby told CNN on Monday.

"But we don't seek a war with Iran. We're not looking for a wider conflict in the Middle East," he added.

Iran said it had nothing to do with the attack and denied US accusations that it supported militant groups responsible for the Sunday strike on the remote frontier base in Jordan's northeast, near the borders with Iraq and Syria.

While Washington is still gathering the facts, "we know it was carried out by radical Iran-backed militant groups operating in Syria and Iraq," Biden said on Sunday, pledging to hold "all those responsible to account at a time and in a manner of our choosing."

Kirby would not speculate on the options being considered by the president, including whether targets inside Iran were on the table.

He said Washington wants to "make it clear" that the attack -- part of a series of other increasingly dangerous assaults by Iran-backed militants in the region in recent weeks -- was "unacceptable."

British Foreign Secretary David Cameron joined Biden on Sunday in blaming "Iran-aligned" militants and called on Tehran to "de-escalate the region."

Iran's foreign ministry spokesman Nasser Kanani has rejected the accusations as "baseless," adding Sunday Tehran "is not involved in the decisions of the resistance groups."

There has so far been no claim of responsibility for the strike, although on Sunday the Islamic Resistance in Iraq claimed to have launched three drone attacks at bases in Syria, including near the Jordanian border.

The group -- a loose alliance of Iran-linked armed groups that oppose US support for Israel in the Gaza conflict and wants them out of Iraq -- has claimed dozens of attacks on US and anti-jihadist coalition forces in Iraq. (AFP)