WASHINGTON—A top commander of U.S. military operations in Syria said he wasn’t informed of any agreements President Donald Trump and Russian President Vladimir Putin reached at their summit this week.

Army Gen. Joseph Votel, commander of U.S. Central Command, which is responsible for the Middle East, said Thursday in a briefing with reporters that he had “no new guidance as a result of Helsinki,” the site of Monday’s summit. Syria was among the topics Messrs. Trump and Putin said they discussed.

On Tuesday, a Russian defense ministry spokesman said the two nations had reached agreements and Russia was ready to discuss “cooperation in Syria.”

But U.S. officials across government have said they aren’t clear what the two leaders agreed upon. The lack of memorandums on the one-on-one, two-hour meeting has left military planners uncertain what was discussed on topics such as stopping Iranian expansion into Syria, Russia’s support for Syrian leader Bashar al-Assad, and the war against Islamic State.

Gen. Votel, however, stressed that he feels the “mission is very, very clear.”