ISLAMABAD: Pakistan accused United States on Thursday of a “slander campaign” against Islamabad over the arrest of a man accused of acting as a Pakistani government agent in the United States.

Ghulam Nabi Fai, 62, a US citizen detained on Tuesday, is suspected of links to a decades-long effort that allegedly funnelled millions of dollars to Washington to lobby US politicians on behalf of Kashmiri causes.

The US Justice Department said Fai and Zaheer Ahmad, 63, a US citizen and resident of Pakistan, faced five years in prison if found guilty.

“Dr Fai is a US citizen. A demarche was made to the US embassy in Islamabad today to register our concerns, in particular the slander campaign against Pakistan,” the ministry of foreign affairs said in a statement.

Fai was arrested on Tuesday morning and set to appear Thursday before a court in Alexandria, near the US capital. Ahmad is believed to be in Pakistan.

“Foreign governments who try to influence the United States by using unregistered agents threaten our national security,” FBI Assistant Director in Charge James McJunkin said.

The influence peddling allegations provoked an angry response from Islamabad.

“Upholding fundamental rights of Kashmiris is the fundamental responsibility of the international community and all conscientious people who value human rights and values,” the statement from Pakistan's foreign ministry added.

“Campaigns to defame the just cause of the Kashmiri people will not affect its legitimacy,” it added.