Protesters denouncing delays in dealing with their asylum claims set fire to facilities used by the European Asylum Support Office (EASO) on the Greek island of Lesbos on Monday.
About 70 people, most from Pakistan and Bangladesh, threw rocks and burning blankets at containers inside the Moria camp, damaging a number of them.
Staff and migrants were safely evacuated. No injuries were reported but a number of arrests were made.
A spokesman for EASO said protesters had hurled petrol bombs while interviews with asylum-seekers were taking place.
EASO staff had evacuated the camp.
“They burnt our offices this morning … The process will not resume for the time being,” he said.
“We have to evaluate security issues and in our view we need more presence of Greece police to be in place.”
Unrest has broken out before among asylum seekers with more than 15,000 living in overcrowded camps on Greek islands close to Turkey, with which the EU has struck a deal to stem the flow.
To avoid being sent back to Turkey under that accord, many migrants have claimed asylum in Greece but they wait for weeks or months for their applications to be processed on a case by case basis.