Though publicly both sides insist their relationship is solid and indispensable, ties between the CIA and Pakistan’s powerful Inter-Services Intelligence (ISI) Agency seem to be suffering in the face of what is being called an “aggressive spy battle.”

Reports from the Associated Press say that the CIA has issued private complaints to the Pakistani government about an apparent attempt by the ISI to plant a “double agent” in the American spy agency.

Reportedly, the CIA was approached by a Pakistani man claiming to have information about Pakistan’s nuclear weapons program, and who came with spent fuel rods from the program. After probing, the CIA decided the man was sent by ISI specifically to infiltrate the CIA and provide data on American spying inside Pakistan. Pakistan promised to “look into” the matter but it appears nothing ever came of it.

The US relation toward the ISI is somewhat bizarre. While officials have endlessly claimed the ISI is providing “direct support” for the Taliban, the CIA is also direct funding the agency, providing upwards of a third of the ISI’s operating budget annually.