He also said the Centre has detected "suspicious amount" worth Rs 3.68 lakh crore in 23.22 lakh accounts in various banks.
"The money deposited in banks post-demonetisation and earlier transactions in those accounts...the details submitted by the bank account holders and their earlier tax returns are not matching hence these are suspicious transactions. The government agencies found 17.73 lakh suspicious transactions due to demonetisation," the Road Transport and Highways Minister told a press conference here.
"We think it is black money", he added.
"For the first time, something like this has happened. Those people had no option but to deposit their money in banks because of demonetisation," the minister said, adding the Income Tax department is carrying out the investigation.
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"This is a huge task and the government agencies are working on it," Gadkari said.
Hailing noteban, Gadkari said it not only helped unearth blackmoney, but also kickstarted the beginning of the new economy.
He said the government agencies found that accounts of 28,000 companies out of 2.97 lakh closed companies were accessed after demonetisation.
Listing various benefits of note ban, Gadkari said the Gross Disposable Income has gone up from 9 per cent to 13.3 per cent.
"The business of mutual funds has also gone up 45 per cent. Demonetisation has helped in industrial and infrastructural growth. Post-November 2016, the demand for personal insurance and first year premium has gone up by 46%," he said.