NEW DELHI -- Having blamed a Pakistani terrorist group for last month's deadly attacks in Mumbai, investigators are turning their attention to homegrown suspects who may have assisted with attacks on Indian soil.

The suspects are thought to have offered help with surveillance, safe houses and border crossings. The potential involvement of Indians complicates India's initial assertion that the Mumbai attacks were carried out solely by Pakistani nationals.

Mumbai police are looking in particular at two Indian suspects in their custody who, they say, were trained by the Pakistani group Lashkar-i-Taiba and who may have helped extremists as they prepared to launch strikes.

Indian police say at least one Indian operative -- Sabauddin Ahmed, 29 -- aided Pakistani extremists by providing safe houses and guiding them across the border to carry out assaults in India.

Although Pakistani extremists once favored Kashmir as their route into India, crossing the border there has become more difficult in recent years, as authorities have cracked down on infiltrators. Indian investigators say they are uncovering information on a vast network of paths into India through Nepal and Bangladesh, as well as the Arabian Sea, the route chosen by the 10 gunmen who carried out the Mumbai attacks.

The use of new land and sea routes, investigators say, has widened the theater of war beyond Kashmir and into the Indian heartland, as well as cosmopolitan cities such as Hyderabad and Bangalore, both of which were recently the scene of bombings.

The focus on possible Indian collaborators comes nearly two weeks after the assault on India's financial capital, in which gunmen opened fire at several sites and laid siege to two luxury hotels and a Jewish prayer center, killing at least 171 people, including six Americans, and wounding more than 230.

Mr. Ahmed is being brought to Mumbai for questioning over his alleged links to Lashkar, the group said to have masterminded the attacks. Indian police earlier this year arrested Mr. Ahmed, along with another suspect, Faheem Ansari, 35, in connection with a grenade attack on a police camp.

In the days after the Mumbai siege, India demanded that Pakistan crack down on the militant groups it suspected of planning the attacks, arrest their leaders and extradite them for trial in India. Pakistan has refused to hand them over, but several have been rounded up in raids. Pakistani Prime Minister Yousaf Raza Gillani yesterday confirmed the arrest of two prominent militant leaders.

The United States has been assisting in India's investigation, Adm. Michael Mullen, chairman of the Joint Chiefs of Staff, said yesterday. "Where we've been asked, we are working with the Indians to provide them intelligence" to prevent such attacks, he said at a Pentagon news conference.

Adm. Mullen said he had discussed with Pakistan's leadership the troubling role of its Inter-Services Intelligence agency.

U.S. military officials have said they have no evidence that the ISI was directly involved in the Mumbai attacks, although Indian officials have suggested a link. Pakistan has denied that anyone in its government was involved.