Dozens of specialists from the US Central Intelligence Agency and Federal Bureau of Investigation are advising the Ukrainian government, a German newspaper reported Sunday.
Citing unnamed German security sources, Bild am Sonntag said the CIA and FBI agents were helping Kiev end the rebellion in the east of Ukraine and set up a functioning security structure.
It said the agents were not directly involved in fighting with pro-Russian militants. "Their activity is limited to the capital Kiev," the paper said.
The FBI agents are also helping the Kiev government fight organised crime, it added.
A group specialised in financial matters is to help trace the wealth of former Ukrainian president Viktor Yanukovych, according to the report.
The interim Kiev government took charge in late February after months of street protests forced the ouster of Kremlin-friendly Yanukovych.
Fierce battles between Ukrainian soldiers and pro-Russian separatists in the country's east have left more than 50 people dead in recent days.
Last month the White House confirmed that CIA director John Brennan had visited Kiev as part of a routine trip to Europe, in a move condemned by Moscow.