Defense Secretary Jim Mattis said Tuesday the U.S. intends to continue backing the Saudi-led coalition fighting Houthi rebels in Yemen despite civilian casualties and questions about the Saudis' commitment to avoiding killing innocents. At a rare Pentagon news conference, Mattis defended U.S. support for the coalition, saying American influence on the Arab air campaign has made a difference in reducing instances of errant bombing and the targeting of civilians. He noted, however, that U.S. support is conditioned on a Saudi commitment to doing "everything humanly possible" to avoid any loss of innocent life and Riyadh supporting a U.N.-brokered peace process to end the civil war. The U.S. provides the Saudis and their United Arab Emirate coalition partners with intelligence, aerial refueling and military advice, but U.S. forces are not directly involved in the airstrikes or other aspects of the fighting. "For the last several years we have been working with the Saudis and the Emiratis, doing what we can to reduce any chance of innocent people being injured or killed," Mattis said. In his first Pentagon news conference in several months, Mattis also said the U.S. might carry out military exercises with South Korea next spring after having cancelled a major exercise this year as a gesture toward advancing diplomacy aimed at eliminating North Korea's nuclear weapons. Mattis said no decision has been made on when to resume military exercises, but his statements suggested that the recent cancellation might not be repeated. "As you know, we took the step to suspend several of the largest exercises as a good-faith measure coming out of the Singapore summit," he said, referring to President Donald Trump's meeting June 12 with North Korean leader Kim Jong Un, which has yet to lead to any denuclearization. "We have no plans at this time to suspend any more exercises." Pressed to say whether he meant to suggest that North Korea has been acting in bad faith since the summit, Mattis said, "No. Not at all." He added, "We are going to see how the negotiations go, and then we'll calculate the future." He said he did not want to influence the diplomacy, although it appears there's been little substantive negotiation on a nuclear deal. A planned trip by Secretary of State Mike Pompeo to Pyongyang was put off last week because of a lack of progress on denuclearization. On Yemen, Mattis said the U.S. supports Saudi Arabia's right to defend its territory against rocket attacks by Houthi rebels in Yemen. He said the Saudi military has been receptive to U.S. advice and training on conducting airstrikes. "At no time have we felt rebuffed or ignored when we bring concerns to them," he said. "The training that we have given them we know has paid off." He cited instances of Saudi pilots deciding during a combat mission to withhold fire to avoid potential civilian casualties, even when they have authority to fire. Criticism of the Saudi campaign surged earlier this month when an airstrike hit a bus, killing dozens, including school children. Among those in Congress calling for the U.S. to pull the plug on support for the coalition is Rep. Ro Khanna, a California Democrat, who has called the bus attack a barbaric act. On the day of the attack he said the U.S. "must end our complicity in this slaughter." Mattis noted the U.S. is pressing the Saudi government to complete an investigation of what went wrong. "We recognize every mistake like this is tragic in every way, but we have not seen any callous disregard by the people we're working with," Mattis said. "So we will continue to work with them." Three experts working for the U.N.'s Human Rights Council said in a report this week that the governments of Yemen, the United Arab Emirates and Saudi Arabia may have been responsible for war crimes during 3 and 1/2 years of fighting against rebels there. Last week, the international rights group Human Rights Watch charged that the Saudi-led coalition had not credibly investigated civilian casualties. It said the coalition's "sham investigations" have fallen short of "international standards regarding transparency, impartiality, and independence." The report highlighted discrepancies between the findings of the coalitions' investigative body, the Joint Incidents Assessments Team, and those by Human Rights Watch. Mattis was also asked about sporadic rumors that the U.S. may consider using private contractors to substitute for U.S. troops in Afghanistan. He said that "when Americans put their nation's credibility on the line privatizing it is probably not a wise idea." Blackwater Worldwide founder Erik Prince has advocated for the use of more military contractors in Afghanistan, and at one point had found some limited backing in the White House.