MUMBAI- India's market regulator is "seriously" looking into the issue of prescient messages on company results circulated by market insiders in private WhatsApp groups, its chairman said on Tuesday, a sign the investigation is gaining momentum.

The comments by Securities and Exchange Board of India (SEBI) Chair Ajay Tyagi come weeks after a Reuters investigation documented at least 12 such cases of prescient messages about major Indian companies.

"The messages are quite close to what has come in results, so it's something we cannot really sit quietly on," said Tyagi.

Citing unidentified sources, the Business Standard newspaper said SEBI had summoned chief financial officers and company secretaries of at least 12 firms over the issue of whether prescient social media messages involving them were being circulated.

The regulator had asked each company official to appear and make a written submission about those given access to the quarterly results and the method used to disseminate price-sensitive information within the company, the paper added.

The executives were asked to explain the measures taken to prevent future occurrences, the paper said, without naming the companies whose officials were summoned.

Tyagi declined to confirm whether the regulator had summoned company executives, but expressed concern about whether such messages were being circulated.

"I wouldn't say whether we summoned (executives) or not, but we are taking this very seriously," he told reporters on the sidelines of an investment banking event.

Exchanges are also cooperating with SEBI and looking into the matter, said Vikram Limaye, chief executive of the National Stock Exchange, India's biggest bourse operator.

"We are working with SEBI, as you would expect," Limaye said at the same event.

The measures included checking for evidence of wrongdoing, involving the dissemination of information ahead of results, as well as providing data to help SEBI's investigation, he added.

The comments confirm a previous source-based Reuters report that exchanges had been asked for trading data on the companies mentioned in the Reuters story.

(Reporting by Rafael Nam; Editing by Euan Rocha and Clarence Fernandez) ((rafael.nam@thomsonreuters.com; +9122-6180-7425; Reuters Messaging: rafael.nam.thomsonreuters.com@reuters.net))