Separate teams of the Enforcement Directorate (ED) conducted search-and-seizure operations across Calcutta, Salt Lake and New Town on Tuesday as part of a probe into alleged money laundering through bank accounts linked to the Trinamool Congress.

Sources in the central agency said the investigation centred on allegations that more than ₹150 crore from the party's bank accounts had been routed through various aviation and travel companies for suspected irregular transactions.

One of the premises searched was the office of an aviation company that had provided chartered flights to Trinamool general secretary Abhishek Banerjee, party chief Mamata Banerjee and other leaders during election campaigns and on other occasions. The company is under the ED's scanner as part of the investigation.

Among the addresses raided were the residence of a Salt Lake-based businessman and an office in central Calcutta, near the Kolkata Police headquarters in Lalbazar.

"The probe is connected to an alleged laundering of funds, and the raids were conducted to collect material evidence under the Prevention of Money Laundering Act (PMLA)," an ED official said.

A section of ED officials said funds of political parties can come under the agency's scanner under specific provisions of the PMLA that deal with offences committed by "companies".

"Since political parties are largely recognised as an association of individuals, the ED and courts treat them as entities that can be prosecuted under anti-money laundering laws," the officer added.

The search-and-seizure operation came within weeks of Aroop Biswas, Trinamool's former treasurer, writing to a private bank on June 12 requesting that the party's accounts be frozen.

The letter prompted a faction of Trinamool leaders, led by Ritabrata Banerjee, to lodge a police complaint alleging that the bank accounts could contain "proceeds of crime".

The three bank accounts were subsequently frozen. A legal battle is underway in Calcutta High Court over ownership of the accounts, which collectively hold around ₹440 crore.

On Tuesday, the court said it will hear the case on Wednesday.

ED sources said the company, which offers chartered flights on hire, has been directed to submit details of its last audited results and a year's bank transactions leading to the Assembly polls in Bengal in May.