The United States is considering ways to boost military support for the Saudi-led fight against Iraninfo-icon-backed rebels in Yemeninfo-icon, believing military pressure is needed to prod the militants into a negotiated end to the conflictinfo-icon, U.S. officials said Wednesday.

The U.S. already is helping the Saudis by providing intelligence and aerial refueling of their combat aircraft. But the coalition, which also includes the United Arab Emiratesinfo-icon, has failed to defeat the rebels known as the Houthis. The rebels seized the capital, Sanaa, and much of northern Yemen in 2014.

International calls for an end to the conflict are intensifying as civilian casualties rise. Healthinfo-icon groups warn that the Arab worldinfo-icon's poorest country is on the brink of famine.

Defense Secretary James Mattis, who met King Salman and other top Saudi officials Tuesday and Wednesday, has complained about Iran sending missiles to the Houthis, who've then used them to fire across Yemen's border into Saudi Arabiainfo-icon.

"Everywhere you look, if there's trouble in the region, you find Iran," Mattis said after his meetings Wednesday. "So right now what we're seeing is the nations in the region and others elsewhere trying to checkmate Iran and the amount of disruption and instability they can cause."

The warinfo-icon has claimed the lives of more than 10,000 civilians and led to the displacement of some 3 million Yemenis. Dozens of Saudi soldiers have been killed in cross-border attacks from Yemen.

Mattis said the U.S. would "reinforce Saudi Arabia's resistance to Iran's mischief" and suggested the possibility of President Donald Trump visiting Saudi Arabia.

"We are not leaving this region," Mattis said.