Turkey has pledged $5 billion while Qatar has pledged $1 billion to help rebuild Iraq after the war on the Islamic State group.
Tillersonsaid the militants are no longer in control of 98 percent of the territory they held at their height in 2014 when they declared the establishment of a caliphate in Iraq and Syria, but that they now pose a different threat.
Tillerson announced $200 million in new aid to liberated areas of Syria.
Tillerson said continued US funding for UNRWA would depend in part on whether other donors step up their contributions.
Tillerson called the package "a signal to the rest of the world that the U.S-Jordan partnership has never been stronger".
"In Iraq and Syria, ISIS is attempting to morph into an insurgency".
Turkey launched a military incursion into Kurdish enclaves in northern Syria last month, drawing criticism from the US and prompting concerns of a potential confrontation between Turkish and American forces in the region. The operation is carried out against Kurdish SDF-affiliated People's Protection Units (YPG), which Ankara believes have links to the Kurdistan Workers' Party (PKK), designated as a terrorist organization in Turkey.
Tillerson, for his part, voiced Washington's appreciation for the Jordanian role in helping to stabilize the region and taking in numerous Syrian refugees.
Tillerson announcement comes after Turkish President Recep Tayyip Erdogan called on the USA earlier in the day to "stop this theater with Daesh in Syria", adding that a decision by the U.S. to continue to fund the Syrian Kurdish YPG militia would affect Turkey's decisions.
"If communities in Iraq and Syria can not return to normal life, we risk the return of conditions that allowed ISIS to take and control vast territory", he said, using an acronym to refer to the group.
Tillerson expressed concern over Saturday's confrontation between Israel and "Iranian assets" in Syria. At the weekend, the Israeli military struck 12 targets in Syria, including four belonging to Iran, after saying that an Iranian drone penetrated its airspace.
Looming in the background is flaring tension between Iran and Israel.
Complicating the picture is Russia's involvement in the conflict, which includes not only declared air and artillery support for Assad's army, but an unknown number of Russian mercenaries embedded with Syrian forces. The fighters have also been largely defeated in neighboring Syria.
US Secretary of States Rex Tillerson declared on Wednesday that Iran must withdraw its forces and militias from Syria.
"I think in terms of this observation that the USA has little leverage or role to play is simply false", Tillerson said at a briefing Tuesday, according to Bloomberg.