WASHINGTON -- In setting the stage for President Trump's first meeting with Russian President Vladimir Putin, Secretary of State Rex Tillerson said the U.S. remains open to working with Russia with an eye toward creating stability and finding a political solution in Syria.

Tillerson declared that the U.S. is "prepared to explore the possibility" of joint on-the-ground operations with Russia in Syria, efforts to maintain areas free of ISIS with no-fly zones, cease-fire observers, and mechanisms that allow deliveries of humanitarian aid.

But Tillerson explained that there are some caveats: he's putting the onus on Russia, as one of Assad's key backers, to safeguard those efforts.

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"Russia, as a guarantor of the Assad regime and an early entrant into the Syrian conflict, has a responsibility to ensure that the needs of the Syrian people are met and that no faction in Syria illegitimately re-takes or occupies areas liberated from ISIS' or other terrorist groups' control," Tillerson wrote on Wednesday.

U.S.-backed forces have been making progress in Raqqa, which ISIS has claimed as its capital. Tillerson said that ISIS may in fact be on the "brink of complete defeat" there.

The Trump administration has not said if there is a plan to discuss a primary sticking point: allegations about Russia's meddling in the U.S. presidential election. This was not a topic Tillerson broached when he visited Russia earlier this year.

In the past Tillerson has described the the U.S.-Russian relationship as being at its lowest point since the Cold War. But he sees Syria as the vehicle in changing that.

"We have been engaged with Russia for some time now to identify areas [where] we should have mutual interest. Syria is certainly one that is a very complex situation," Tillerson told reporters at Joint Base Andrews before departing on his flight for Hamburg.

There is no formal agreement yet to work together in Syria.

"We're at the very beginning," he said of Mr. Trump's meeting with Putin. He feels it's necessary that the leaders have a "good exchange" over the nature of their relationship, and he said that Russia's intentions with the U.S. remain to be seen.

While Tillerson acknowledged that the two countries have "unresolved differences" neither his written statement nor his on camera remarks referenced the recent U.S. pursuit of pro-regime forces in Syria. As a result of provocative and violent acts of the regime forces, the U.S. has retaliated with four strikes in the last two months. These attacks have added an element of friction to U.S.-Russia relations. Russia's foreign minister last week said that Moscow would respond to what it viewed as a U.S. provocation -- its statement warning the Assad regime against carrying out another chemical attack -- "proportionally and with dignity."

The Trump administration has not called for regime change in Syria. Instead it has stated that the future of the country should be determined by the Syrian people. Russia remains a supporter of the regime. Just last week Assad visited a Russian air base in western Syria.