Leader of Pakistan's Muttahida Qaumi Movement (MQM) party Altaf Hussain was arrested in London Tuesday on charges of money laundering, a media report said.
The London Metropolitan Police said that a 60-year-old man has been arrested from a north-west London property on charges of money-laundering, but they declined to disclose the exact identity for "legal reasons", Dawn online reported Tuesday.
Police said that a search operation was underway at the property in north-west London.
Speaking to DawnNews, London-based journalist Farooq Shah said Hussain has been arrested and the police were searching his house.
DawnNews quoted the Scotland Yard as saying that the investigation would continue for 24 hours.
Altaf Hussain is the founder and chief of the Muttahida Qaumi Movement (MQM), its stronghold being Karachi port city in southern Pakistan.
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Hussain has been living in London in self-exile for the past 20 years.
In the early 1990s, the MQM chief went into exile as the Pakistani government at the time conducted an operation in Karachi.
The operation, said to be directed against "terrorist" and "criminal" elements in Karachi, resulted in effectively becoming action against the MQM and with it Karachi was caught in the middle of a war involving law enforcement agencies and political parties.
Hussain's elder brother Nasir Hussain and nephew Arif Hussain were killed during this period of violence.
In April this year, the MQM joined the state government in Pakistan's Sindh province, led by Pakistan Peoples Party (PPP).
As the news of Hussain's arrest spread in Karachi, panicked shop-keepers and stall-owners rushed to close their businesses for fear of violence, Dawn online reported.
In the wake of the frenzy in the city, the Karachi Chamber of Commerce and Industry (KCCI) demanded that the provincial capital be handed over to military control, and added that if the government failed to establish peace in the next 24 hours, a strike would be observed, the report said.
Prime Minister Nawaz Sharif said the issue of Hussain's arrest was of an extremely sensitive nature, and that the government would take all legal angles into account.
The premier has directed parliamentarians and members of the ruling Pakistan Muslim League (Nawaz) not to comment on the news.
The London Metropolitan Police had initiated investigations against Hussain on charges of money laundering and incitement to violence in July 2013.
The Metropolitan Police had then confirmed that "a considerable amount of money" had been found during raids on Hussain's residence and office in London.