U.S. Secretary of Defense Jim Mattis, second from left, is greeted by U.S. Ambassador Douglas Silliman as he arrives at Baghdad International Airport, Iraq, on an unannounced trip Monday, Feb. 20, 2017.

Defense Secretary Jim Mattis said Monday he believes US forces will be in Iraq and in the fight against ISIS militants for a while, despite some rocky times between the two nations.

Speaking at the end of a day of meetings in Baghdad with military commanders and Iraqi political leaders, Mattis said he is open to any request from his military commanders to aid the battle to retake Mosul and launch a major battle to oust IS from the base of its so-called caliphate in Raqqa, Syria. He would not provide details.

Despite President Donald Trump’s past threats to take Iraq’s oil and his attempt to impose a travel ban that includes Iraqi citizens, Mattis said his meetings with Iraqi leaders underscored the partnership the US has with the Iraqis.

He said there’s no doubt that “the Iraqi people, the Iraqi military and the Iraqi political leadership recognize what they’re up against and the value of the coalition and the partnership, in particular with the United States.”

His optimistic words come on the heels of his earlier declaration that the U.S. does not intend to seize Iraqi oil, distancing himself from comments made by President Donald Trump that has rattled Iraq’s leaders.

Trump’s oil threat and his inclusion of Iraq in the administration’s travel ban have roiled the nation and spurred local lawmakers to pressure al-Abadi to reduce cooperation with Washington.

“I think all of us here in this room, all of us in America have generally paid for our gas and oil all along, and I’m sure that we will continue to do that in the future,” Mattis told reporters traveling with him. “We’re not in Iraq to seize anybody’s oil.”

Trump brought up the prospect during the campaign, and he mentioned it again late last month during a visit to the CIA. He told the gathering there that, “To the victor belong the spoils,” and added, “maybe you’ll have another chance” to take the oil.

Despite those tensions, Mattis and Lt. Gen. Stephen Townsend, the top US commander in Iraq, described an enduring partnership between the US and Iraq.

“I imagine we’ll be in this fight for a while and we’ll stand by each other,” Mattis said.

Townsend, who was standing by Mattis, declined to say how long the US will stay in Iraq. But, he said, “I don’t anticipate that we’ll be asked to leave by the government of Iraq immediately after Mosul.” He added, “I think that the government of Iraq realizes their very complex fight, and they’re going to need the assistance of the coalition even beyond Mosul.”

Townsend also acknowledged that US forces are now operating closer and deeper into the fight with Iraq units as the battle to retake western Mosul entered its second day.

He said the change began in recent months during the successful fight to take back eastern Mosul, and is now happening more often. US special operations forces have been working with the Iraqis, offering advice and assistance but initially they were only at the headquarters’ level.

More recently they have been moving closer to the battlefront, working with brigade, battalion and sometimes smaller units. But they are generally with command and control units, not in combat on the front lines.

“We embedded advisers a bit further down into the formation,” Townsend said.

Mattis’ unannounced one-day stop in Iraq was his first as Pentagon chief and the first visit to the warzone by a senior member of the Trump administration. It comes as Mattis and his military leaders are nearing the end of a 30-day review of the Islamic State fight. He must send Trump a strategy to accelerate the battle in the next seven days.

Senior US military officers said Monday that the fight in the more urban, heavily populated areas of western Mosul will require more precision airstrikes and probably smaller bombs that can take out a building or group of militants and leave surroundings intact.

Lt. Gen. Jeff Harrigian, the top Air Force commander in the Middle East, said troops responsible for calling in airstrikes are closer to the fight and can move forward with Iraqi units. They also have greater authority now to speak directly to pilots in the aircraft overhead, allowing them to launch strikes more quickly, he said.

Military leaders, said Harrigian, realized they could be more responsive now because the troops have built up trust with their Iraqi partners.

While Mattis and Townsend wouldn’t talk about any future changes or accelerants in the war fight, various military options have been discussed in recent months. Among them: putting more troops in Iraq and Syria and boosting military aid to Kurdish fighters backed by the US-led coalition.

More specifically, officials have talked about expanding efforts to train, advise and enable local Iraqi and Syrian forces, increasing intelligence and surveillance, and allowing US troops to move forward more frequently with Iraqi soldiers nearer the front lines.

The Pentagon also would like more freedom to make daily decisions about how it fights the enemy. Current and former US officials discussed the likely options on condition of anonymity because they weren’t authorized to talk publicly.

In Syria, a possible option would be to send more US forces, including combat troops, there as the Raqqa fight heats up.

Another move would be to provide heavy weapons and vehicles to the U.S.-backed Syrian Kurds, and boost training. They have been the most effective force against IS in northern and eastern Syria, but the proposal is sensitive. Turkey, a key U.S. and NATO ally, considers the group a terrorist organization.