NAIROBI, Kenya — Supporters of Kenya’s main opposition leader burned an American flag near the United States Embassy and marched to the building’s gate on Friday, two days after youth leaders threatened the American ambassador.

The demonstration came at a time of growing frustration among opposition supporters with United States policy in Kenya. They say the American government has unfairly criticized the opposition leader, Raila Odinga, and they are impatient with American demands that Mr. Odinga accept the results of last year’s presidential election, which handed his longtime rival, Uhuru Kenyatta, a second term.

About a dozen supporters of Mr. Odinga carried signs that said, among other things, “Godec must go” — referring to the United States ambassador, Robert F. Godec — and marched less than half a mile to the embassy.

The group, which eventually grew to about 20 people, demonstrated for under a half-hour before Dan Travis, the acting deputy United States ambassador, emerged and invited three members inside to meet with the ambassador. They declined.