Holding a banner reading "Unpunished Crime," but also pictures of war crimes suspect Radovan Karadzic and Serbian flags, the protesters briefly blocked traffic in one of the main streets in the Serbian capital.
Dozens of riot police had been deployed in the city center and around the two embassy buildings. No violence was reported.
The U.S. Embassy in Belgrade was set on fire and damaged during the protests in February against the U.S.-backed independence of Kosovo.
Last week's protests against the arrest of former Bosnian Serb leader Karadzic also had turned violent. About 80 people were injured in clashes between the police and the rioters.
Karadzic was arrested by the pro-Western Serbian government. He was sought on genocide charges by a UN war crimes tribunal, but nationalists at home consider him a hero.
Also Monday, government minister Rasim Ljajic said tens of thousands of refugees who still remain displaced after the Yugoslav wars should return to their homes in other Balkan nations.
Ljajic said there could be no reconciliation in the region "before the closing of the refugee files." He added that Belgrade would initiate a meeting with Croatia and Bosnia on the issue.
While thousands of Serbs have returned to Croatia since the war, many more remain in Serbia.
A Message from The Moscow Times:
Dear readers,
We are facing unprecedented challenges. Russia's Prosecutor General's Office has designated The Moscow Times as an "undesirable" organization, criminalizing our work and putting our staff at risk of prosecution. This follows our earlier unjust labeling as a "foreign agent."
These actions are direct attempts to silence independent journalism in Russia. The authorities claim our work "discredits the decisions of the Russian leadership." We see things differently: we strive to provide accurate, unbiased reporting on Russia.
We, the journalists of The Moscow Times, refuse to be silenced. But to continue our work, we need your help.
Your support, no matter how small, makes a world of difference. If you can, please support us monthly starting from just $2. It's quick to set up, and every contribution makes a significant impact.
By supporting The Moscow Times, you're defending open, independent journalism in the face of repression. Thank you for standing with us.
Remind me later.