Recounting Secretary of State John Kerry's visit to the country, Duterte, speaking Tagalog, said that he was feuding with US Ambassador Philip Goldberg.
"I was with (incoming defense chief General) Delfin Lorenzana. We talked to Kerry, he was actually OK because I had a fight with his ambassador. I told him: 'your ambassador is a gay son of a bitch.'"
"I was annoyed at him, for interfering in the elections, giving statements here and there. He wasn't supposed to do that."
He also called Kerry "crazy" and suggested that he "offend" him more to get more aid.
"Kerry came here, we had a meal, and he left me and Delfin $33 million. I said, OK, maybe we should offend them more, so this crazy will just give more money, just to make peace. So, it's all about the money."
Duterte's comments came as he addressed troops at the country's Armed Forces Central Command Headquarters on August 5.
US State Department spokeswoman Elizabeth Trudeau said the department had summoned the Filipino chargé d'affaires to "clarify" Duterte's remarks.
"We have asked the Philippines chargé to come into the State Department to clarify those remarks," she said at a briefing.
Goldberg has been the US ambassador to the Philippines since November 2013.
President known for straight talk
It's the latest offensive remark from Duterte, a leader not known for his diplomacy.
He took office at the end of June, after campaigning on a platform of tough policies on drugs and crime. The former mayor of Davao, a restive city in the southern Philippines, has long had a reputation for straight-talking and using offensive language.
On the campaign trail, he found himself having to defend comments made in 1989 regarding the rape and murder of an Australian missionary in a prison in Davao when he was the mayor.
"I was angry she was raped, yes, that was one thing. But she was so beautiful, I think the mayor should have been first. What a waste," he said of the attack.
He repeatedly refused to apologize for the comments and told the ambassadors of the United States and Australia, two of the Philippines' closest allies, to "shut their mouth
" after they criticized his "joke." He also disowned an apology
that was issued on his behalf by his political party.
He also cursed the Pope
for traffic problems caused by the pontiff's visit to the Philippines.
"We were affected by the traffic. It took us five hours. I asked why, they said it was closed. I asked who is coming. They answered, the Pope. I wanted to call him, "Pope, (swear words), go home. Do not visit us again," he said.
The comments come as the President appears to have made a threat to reinstate martial law in the country, if the Supreme Court attempts to thwart his war on drugs.
Speaking to troops on the restive island of Mindanao Tuesday, he said: "If this (attempt to thwart the war on drugs) continues, you want to stop me, well then... if all goes awry, or would you rather that I declare martial law?"
During periods of dictator Ferdinand Marcos' 21-year-long leadership, the country was under martial law. Duterte also recently approved the burial of the former leader
in the National Heroes' Cemetery.