ISLAMABAD (Agencies) - 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 Kashmiri-born US citizen detained 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. Dr Fai is a US citizen. A demarche was made to the US Embassy in Islamabad Thursday to register our concerns, in particular the slander campaign against Pakistan, the Ministry of Foreign Affairs said in a statement. 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 added. Campaigns to defame the just cause of the Kashmiri people will not affect its legitimacy, it added. Meanwhile, Kashmiri leader slammed the arrest and called it unfortunate. It is unfortunate that a leader like Fai is being dubbed an agent. He has been representing Kashmiris at various forums to make the world hear our views, said Shabir Shah, a senior separatist in Kashmir. We strongly condemn his arrest. It is aimed at suppressing the voices who call for Kashmirs freedom from India, Shah told AFP. Hardline Kashmiri separatist Syed Ali Geelani said: It has been done at the behest of India and under a conspiracy to weaken the movement of Kashmiris at the diplomatic level. But Kashmir police chief Kuldeep Khoda said Fai had long been a suspect. He has been figuring in lots of things in the past, like what the US has already conveyed, the diversion of Pakistani funds for anti-national activities in India and particularly in Jammu and Kashmir, Khoda alleged. Monitoring Desk adds: Indian security agencies would study the charges brought up against Ghulam Nabi Fai to question the Kashmiri leaders who remained in touch with the Kashmiri leader. Sources in Indian Home Ministry said the charges against Ghulam Nabi Fai are being studied before any decision on possible questioning of some human rights activists and Kashmiri separatist leaders here who had links with him. While lobbying is not illegal in the US, the law requires that the source of funding be disclosed. Fais group, Kashmir American Council, is best known for organising an annual Kashmir peace conference on Capitol Hill in the US, for which he would invite participants - separatist leaders, activists, academicians, journalists - from India and Pakistan. Among the regulars at Fais meetings were moderate Hurriyat Conference chairman Mirwaiz Umar Farooq. He faces possible questioning from the security agencies for suspected links with Fai. Others who have enjoyed Fais fully-paid trips to Washington at least once include head of the government-appointed panel of interlocutors for Kashmir Dileep Padgaonkar and veteran journalist Kuldip Nayar. Nayar told an agency that he never suspected Fai, otherwise a rich man, to be an ISI spy. I have attended his conference long time back. The accomodation he provided to the participants was modest. But at the seminar, also attended by Pakistanis, there was nothing like anti-India voices. I also spoke freely whatever I wanted to, said Nayar. Nayar, a former Indian high commissioner to the UK, said he was rather surprised with the timing of his arrest. They say he has been working for the ISI for the last two decades. Why arrest him now? That too when the honeymoon between the US and Pakistan is getting over.