India's top crypto app CoinSwitch is cooperating with the national financial-crime agency, whose agents searched its offices this week to find out about its business model and user-onboarding processes, its CEO told Reuters on Saturday.

CoinSwitch, valued at $1.9 billion, says it is the largest crypto company in India, with more than 18 million registered users. The firm is backed by Andreessen Horowitz, Tiger Global and Coinbase Ventures.

Ashish Singhal, speaking for the first time publicly about Thursday's search, said his company was engaging with the Indian Enforcement Directorate's unit in the tech hub Bengaluru on functioning of its crypto platform.

"Most of their engagement with us has been about knowing what CoinSwitch does," Singhal said, saying the inquiries included operations of crypto exchanges, how users were onboarded and details about know-your-customer norms.

A person with direct knowledge said the case relates to suspected violations of India's foreign exchange laws. Agents asked about foreign investments, income and outflows to check on compliance, and seized financial documents, the source said.

Singhal declined to specify the agency's allegations, citing legal sensitivities.

The Enforcement Directorate did not immediately respond to a request for comment.

The investigation into CoinSwitch comes amid tightening regulatory scrutiny of the crypto sector in India.

In a separate case the agency this month froze $8 million in assets of WazirX, a top virtual currency exchange, in an investigation of a possible role in helping instant loan app companies launder the proceeds of crime by converting them into cryptocurrencies on its platform.

WazirX disputes the allegations.

The agency has said it was conducting money-laundering investigations against several shadow banks and their fintech companies for potential violations of central bank norms and predatory lending practices.

The CoinSwitch search was "not about money laundering," Singhal said. The agency "has been engaged with us with respect to functioning of our crypto platform and we are fully cooperating with them," he said.

While no official data is available on the size of India's crypto market, CoinSwitch estimates the number of investors at up to 20 million, with total holdings of about $6 billion.