Crackdown on black money by the Narendra Modi government has resulted in finding undisclosed income of over Rs 16,000 crore over the past 20 months, according to a top official.

Besides, assets worth Rs 1,200 crore have been seized since March 2015, according to Revenue Secretary Hasmukh Adhia.

"The present government is very serious on the issue of black money. Various pronouncements of Prime Minister Narendra Modi and Finance Minister Arun Jaitley have made it very clear that this government does not want to spare any effort to bring people with black money to book," Hasmukh Adhia said.

The initiative taken by the government to unearth undisclosed wealth in the country made people declare worth over Rs 4,160 crore and it estimates to receive Rs 2,500 crore in the form of tax and penalties by end-December, he told PTI.

"Prosecution has been filed in 774 cases (up to September 2015)," he said.

The NDA government had promised to bring back black money stashed outside the country during its election campaign last May. Earlier this year, the government had enacted the Black Money (Undisclosed Foreign Income and Assets) and Imposition of Tax Act, 2015, which stipulated stringent punishment and penalty for holding illegal money.

"The last date for paying income tax for those people who made disclosures under the Black Money Act is December 31, 2015. We are hopeful of getting approximately Rs 2,500 crore as tax in the current year," he said.

In May, a study by Global Financial Integrity (GFI) said that illegal money -- made by committing crimes, taking bribes, and evading taxes -- stashed outside the country exceeds the Indian government's annual spending on education or health.

As part of its efforts to put a check on black money, the government has made producing permanent account number (PAN) card details for cash purchases exceeding a certain limit mandatory.

In October, Finance Minister Arun Jaitley had said that "the bulk of black money was still within the country."

The Modi government has also been requesting information about many individuals from the Swiss authorities since last year and the Swiss government has already disclosed the names of a few Indian individuals who have bank accounts in their country.

Calling the government's drive to unearth black money held by the country's citizens a "joke", former director of Infosys T V Mohandas Pai had recently said that the government does not have enough policy, as well as legal and intelligence strength, to deal with the issue.