NEW DELHI, Sept 17 (Reuters) - India has long faced attacks from Pakistan-based militant outfits, but the involvement of home-grown Islamist groups is now adding a "new dimension" to the problem, Prime Minister Manhoman Singh said on Wednesday.

Singh's comment is an explicit, high-level acknowledgement home-grown groups were now carrying out bombings in India, which has traditionally blamed Pakistan for violent attacks on its soil.

In recent months New Delhi has become more cautious about making allegations against Pakistan, and, instead has spoken of the complicity of home-grown Islamists in recent attacks, including a weekend bombing in New Delhi that killed 22 people.

"The role of Pakistan-based terrorist groups cannot be minimised but the involvement of local elements in recent blasts adds a new dimension to the terrorist threat," Singh told a meeting of governors of Indian states.

"We have reports that certain Pakistan-based terrorist outfits are constantly seeking to set up new terrorist modules within our country. This is a matter of utmost concern."

The Indian Mujahideen militant group, which says it carried out several major attacks in recent months to avenge "atrocities" against Muslims in India, said it was responsible for the bombs in New Delhi.

The group sent emails to media outlets denying the Indian government's initial claims that it was actually a front for Pakistan-based militant organisations.

Indian security analysts say although Indian radicals may share the violent and anti-Western ideology of Islamist extremists around the world, their motivation is rooted in a sense of injustice at home.

Their most powerful recruiting tool has been the 2002 riots in the western state of Gujarat where human rights group say around 2,500 people, mostly Muslims, were hacked and burnt to death.

After the deadly train bombings in the western Indian city of Mumbai in 2006, Singh said the alienation felt by many Muslims was worsening matters.

He said on Wednesday India had tightened security on its borders to prevent attacks.

"But in view of the growing involvement of local elements, this is not enough," he said, calling for "vast gaps" in intelligence apparatus to be bridged.

He said certain suggestions were being considered, including the setting up of dedicated anti-terrorism agencies and tougher laws. (Reporting by Krittivas Mukherjee; Editing by Simon Denyer and Jeremy Laurence)

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