The operation launched by Pakistani security forces against banned militant groups, including the Lashkar-e-Tayiba, will continue till the desired results are achieved, officials said on Tuesday.

Lashkar operational commander Zakiur Rehman Lakhwi, accused of masterminding the Mumbai terror attacks, is among more than 20 activists of the Lashkar and its front organisation Jamaat-ud-Dawah who have been arrested since the crackdown began on Sunday, sources said.

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Major-General Athar Abbas, the director general of Inter-Services public relations, said there is no timeframe for the operation and it will continue across the country till the desired results were achieved.

Abbas told the Dawn newspaper that the operation is underway in Muzaffarbad, the capital of Pakistan-occupied Kashmir, and some other parts of the country. He did not identify the areas where the crackdown would be launched. The Lashkar has a sprawling headquarters in Muridke, just outside Lahore [Images].

Abbas said some arrests have been made, including a top man of the Lashkar. The Dawn quoted officials as saying they expected more arrests in the coming days. The newspaper also quoted an unnamed senior security official as confirming that Lakhwi was among two dozen people who had been arrested.

The Pakistan Army [Images] on Monday confirmed that a crackdown had been launched against banned militant groups and said the law enforcement agencies have arrested an unspecified number of people in an intelligence-led operation.

The operation was carried out by army troops backed by a helicopter gunship. Reports said there was an exchange of fire between the militants and security forces. Local residents said they had heard two to three explosions.

The crackdown came after two American leaders, Secretary of State Condoleezza Rice [Images] and Senator John McCain [Images], and a top defence official Admiral Mike Mullen, the chairman of the Joint Chiefs of Staff, visited Islamabad [Images] and asked the country's top leadership to act against Pakistan-based elements linked to the Mumbai attacks.