Arrests in New Delhi and Kolkota linked to supply of SIM cards to militants who carried out attacks.
Indian police on Saturday questioned two men suspected of helping the militants who carried out the Mumbai attacks, amid reports of a home-grown terror link and fresh security jitters.
Pakistan meanwhile said it was awaiting "concrete proof" that a group based there carried out the Nov. 26 to 29 attacks on India's financial capital which killed 172 people, including nine attackers.
The arrests of the two men late Friday are believed to be the first in connection with the attacks, other than the capture of one of the militants during the 60-hour siege.
The men - identified as Tousif Rahaman and Sheikh Muktar - were held "for allegedly providing SIM cards to the terrorists in the Mumbai attacks," senior Kolkata police official Javed Shamim told reporters.
Rahaman, who was arrested in Kolkata, "bought about 40 SIM cards from the city, two of which are believed to have been given to the terrorists," he added.
Shamim said Muktar - who was detained in New Delhi - was from revolt-hit Indian Kashmir, where Islamic militants have been waging a nearly two-decade battle against New Delhi's rule in the disputed Himalayan region.
The pair appeared in a Kolkata court Saturday and were remanded in custody for two weeks on accusations of forgery and cheating.
India has accused Pakistan of harbouring Islamists who trained and equipped the 10 militants, straining ties between the nuclear-armed neighbours and threatening a slow-moving peace process.
Suspicion has fallen on the Pakistan-based Lashkar-e-Taiba (LeT), which has fought Indian control of divided Kashmir and was blamed for a 2001 attack on the Indian parliament which brought the two countries to the brink of war.
Several Indian newspapers on Friday cited unidentified intelligence sources as saying that Pakistan's powerful spy agency, the Inter-Services Intelligence (ISI), was involved in training the gunmen.
Pakistan's President Asif Ali Zardari said in Istanbul on Friday, where he met Afghan counterpart Hamid Karzai, that Islamabad was conducting its own probe into the attacks and "waiting for concrete proof" of LeT's involvement.
"Our position is that we have always been and still are the victims of terrorism," Zardari said.
Pakistan was put on high alert last weekend after a hoax caller pretending to be India's foreign minister Pranab Mukherjee contacted Zardari to warn that India would take military action if it did not hand over those responsible.
The Dawn newspaper, quoting diplomatic and security sources, said that prompted a flurry of activity, as some world leaders feared the row would escalate into war.
Indian media reports Saturday claimed a suspected LeT operative being held in northern Uttar Pradesh state who was arrested in February staged reconnaissance missions in Mumbai, including at the main railway station.
The Chhatrapati Shivaji Terminus was one of a number of locations raked by automatic gunfire and grenade blasts during the attacks.
Other reports said the Indian national, identified as Fahim Ansari, was found with hand-drawn maps of key Mumbai landmarks.
Mumbai's crime branch wants "to interrogate him in connection with the attacks" and see whether he provided any information to the militants, Joint Commissioner of Police (Crime) Rakesh Maria said.
In Vienna, officials said they would probe reports that militants used an Austrian mobile phone number during the siege.
High security meanwhile remained in place at India's major airports after warnings of aircraft hijackings, while police were on alert for the anniversary of the controversial razing of a mosque in the north of the country.
Police said more officers were on streets, at railway stations and government buildings 16 years to the day since Hindu extremists demolished the Babri mosque at Ayodhya, claiming it was built on the site of a temple.
Their actions ignited widespread violence between Hindus and Muslims, including in Mumbai. Some 2,000 people were killed.