The Pakistani government has formally protested Washington's move to arrest a man accused of spying to influence U.S. policy on Kashmir.

A demarche issued on Thursday to the U.S. Embassy in Islamabad shows Pakistan's concerns over what it called the slander campaign against Pakistan in the U.S., said a statement. Currently, Pakistan's embassy in Washington is investigating the matter, reports said.

Syed Ghulam Nabi Fai, a US citizen of Kashmir origin and the executive director of Kashmir American Council, was detained by the U.S. authorities on Tuesday on charges of being an unregistered agent of a foreign government.

The Foreign Agents Registration Act (FARA) of 1938 requires persons acting as agents of foreign principals in a political or quasi-political capacity to make periodic public disclosure of their relationship with the foreign principal, as well as activities, receipts and disbursements in support of those activities.

The FARA Registration Unit of the Counter-espionage Section (CES) in the National Security Division (NSD) can arrest those agents who are not registered under the Act but carry out their operations in disguise.

The U.S. Department of Justice said on Tuesday that Fai lobbied American lawmakers on Kashmir by receiving $4 million from the Pakistani government, including ISI, the country's military spy agency.

Fai was arrested at his home in Fairfax, Virginia on Tuesday. Fai, 62, has also advocated against the Indian rule in Kashmir, which is claimed by both India and Pakistan. Fai's arrest came at a time when relations between Pakistan and the U.S. are already tensed over the killing of Osama bin-Laden on May 2.