"These were forces moving into more advanced positions, too close".
However, Mattis added, both sides drew back after deconfliction discussions between USA officials and their Russian counterparts.
In a statement released by the US Defense Department, Mattis also appreciated Indonesia's support for reconciliation efforts in Afghanistan.
Calling Indonesia "a like-minded partner with shared democratic values and interests", Mattis said the United States greatly values the military relationship between the two nations, noting that Indonesians are supported in their interest and respect for global law, for territorial integrity in the South China Sea, and for their sovereignty. "We have also drawn off slightly". The pro-Syrian government troops had amassed near Deir ez-Zor in the same area where pro-government forces attempted to attack the US-led coalition in February.
When the opposing forces attacked, the United States unleashed hours of strikes and killed about 300 men in a major incident that both Russian Federation and the United States sought to publicly downplay.
"I still can not answer that question", Mattis said.
"The potential for a clash there [in Syria] has, thanks to the Russian direction... been reduced", Mattis said on Tuesday.
Pockets of IS fighters remained holed up in parts of the Middle Euphrates River Valley, and USA officials say efforts to clear them out have stalled, due to Turkey's military incursion against other Kurdish forces in the Afrin area of northwestern Syria.
The U.S. has about 2,000 troops in Syria, many working with the largely Kurdish Syrian Democratic Forces in an effort to eradicate the Islamic State terror group.
Turkey has said it will drive the Kurdish YPG militia away from the Syrian border if it does not reach an agreement with the United States on a plan to remove the group from the Manbij region.