Secretary of State Mike Pompeo on Friday warned Iran not to scuttle an upcoming agreement with the Taliban, accusing the US adversary of seeking to be a "spoiler."
Pompeo confirmed that a one-week partial truce was holding with the Taliban, who are scheduled to sign the landmark accord with the United States in Qatar on Saturday.
"There is a history of Iran engaging in activity inside of Afghanistan to act as a spoiler," Pompeo told the House Foreign Affairs Committee.
"We've seen just these last six days a significant reduction in violence in Afghanistan and we are watching closely to see if the Islamic Republic of Iran begins to take even more active measure that undermine our efforts at peace and reconciliation," he said.
He warned that Iran could increase risks for US troops, whose numbers are expected to be sharply scaled down under the Doha agreement.
Iran's Shiite clerical regime has been historically opposed to the Taliban, which practices an austere brand of Sunni Islam, and quietly backed the 2001 US-led invasion that toppled the Taliban regime.
Iran was part of a coalition that backed the anti-Taliban Northern Alliance and in 1998 amassed troops near the Afghan border after a Taliban assault on Iran's consulate in Herat.
But Iran has increasingly been involved in proxy conflicts with the United States elsewhere, notably in Iraq.
Iran has been mostly cautious in its recent comments on Afghanistan.
But Foreign Minister Javad Zarif last year criticized the US talks with the Taliban, saying they only boosted the extremists and alienated the internationally backed government.