WASHINGTON (Reuters) - The U.S. military signaled on Tuesday it would continue its assistance to the Saudi-led coalition fighting in Yemen, even as it acknowledged U.S. support was not “unconditional” amid mounting concern about the war’s toll on civilians.

Saudi Arabia is leading a Western-backed alliance of Sunni Muslim Arab states trying to restore the internationally recognized government of Yemeni President Abd-Rabbu Mansour Hadi, ousted from the capital Sanaa by the Iran-aligned Houthis in 2015.

The United States and other Western powers provide arms and intelligence to the alliance. Human rights groups have criticized them over coalition air strikes that have killed hundreds of civilians at hospitals, schools and markets.

A Saudi-led coalition air strike that hit a bus earlier this month killed dozens of children, sparking outrage from U.N. officials. Saudi Arabia has said it will investigate the attack.

Mattis dispatched a three-star general to Saudi Arabia after that incident, and told reporters on Tuesday the United States recognized such mistakes were tragic. But he added: “We haven’t seen any callous disregard by the people we’re working with.”

“So, we will continue to work with them, reduce this tragedy,” Mattis said.

The Pentagon believes that its assistance, which includes refueling coalition jets and training in targeting, helps reduce civilian casualties.

In Geneva, U.N. human rights experts said on Tuesday that air strikes by the Saudi-led coalition in the war have caused heavy civilian casualties and that some may amount to war crimes.

The experts’ panel also said fighters of the rebel Houthi movement had fired missiles into Saudi Arabia and shelled the Yemeni city of Taiz.

“Our conduct there is to try to keep the human cost of innocents being killed accidentally to the absolute minimum. That is our goal where we engage with the coalition,” Mattis said.

“Our goal is to reduce this tragedy and to get it to the U.N.- brokered table as quickly as possible.”

The Yemen war is seen as a proxy conflict between the region’s two main powers: Sunni Muslim Saudi Arabia and Shi’ite Muslim Iran.