Police investigating the Mumbai terror attacks have detained two suspected blackmarket cellphone dealers in Calcutta, reported CNN.
An Indian Border Security Force soldier patrols Agartala Airport, Tripura, which like many Indian airports is on high alert.
Authorities are also investigating a man arrested last February with maps and drawings of some of the locations attacked during last month's assault on India's financial capital, which left at least 179 people dead.
The two men arrested in Calcutta on charges of illegally purchasing cellphone SIM cards are being questioned by police who want to know if they sold cards used by the Mumbai gunmen, according to Calcutta Deputy Police Commissioner Jawad Shamim.
Intelligence experts say cellphone SIM cards would allow terrorists to easily switch cellphones and throw pursuers off their trail.
Indian security sources told CNN sister network CNN-IBN Thursday that a Bangladeshi national bought cellphone SIM cards for the attackers at several locations inside India.
Shamim suggested reporters should not jump to any conclusions about a connection to the attack, but acknowledged unconfirmed suspicions that one of the slain terrorists carried a SIM card activated in Calcutta. "It's now up to the Mumbai police to investigate," Shamim said.
Meanwhile an Indian man arrested with five foreigners in north India last February was found to have sketches and maps of several Mumbai locations attacked last month.
Faheem Ahmed Ansari -- who carried a fake Pakistani passport but was an Indian citizen -- is in jail awaiting trial on charges of planning a suicide attack on Mumbai's stock market and the Churchgate railway station.
At the time of the men's arrest, Amitabh Yash, senior superintendent of police in Uttar Pradesh, called the arrest of the six men "very significant," adding: "Generally, we catch two or three of them, the rest manage to escape.
"But then, this is also a warning because that tells us how extensive the network is," Yash said. "And you can be sure there will be other(s)."
Indian authorities believe all the attackers were Pakistanis, specifically blaming Lashkar-e-Tayyiba (LeT), an Islamic militant group based in Pakistan. LeT has denied any responsibility for the attacks, but the sole surviving gunmen told interrogators he was trained by LeT, Indian authorities have said.
Pakistani authorities deny the attackers were from their country, instead blaming what they call "non-state" actors.
Indian officials have previously said the attacks were carried out by outsiders -- but analysts say the latest developments in Calcutta and Uttar Pradesh suggest investigators are also looking at homegrown terrorist connections as well as militants from Bangladesh and Pakistan.
"They needed people on the ground who could guide them and provided the inside dope," said Shuja Nawaz, author of "Crossed Swords," which analyzes the role of Pakistan's military in the country's politics. "Otherwise, the Lashkar doesn't have the capacity to have cased the joints, to have made all these plans and get these people into the target area so effectively."
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Indian security officials have been heavily criticized since the attacks for not heeding the warning signs.
On Friday Home Minister Palaniappan Chidambaram, India's top law enforcement official, admitted that there were government "lapses" during the attacks.