SHANGHAI -- The Shenzhen Stock Exchange said on Friday that it has taken regulatory measures against accounts associated with China Evergrande Group, the country's largest property developer, on suspicion of abnormal trading.

China Evergrande Group is accused of engaging in short-term speculation in a handful stocks through related accounts as well as abnormal trading in rival China Vanke Co. that caused a significant swing in the latter's share price and trading volume, the stock exchange said in a post on its microblog Friday.

The company did not immediately respond to a request for comment.

The announcement came after China's insurance regulator on Tuesday criticized Evergrande Life Insurance, a subsidiary of the conglomerate China Evergrande Group, for what it said was frequent, short-term stock trading.

The Shenzhen exchange said Friday it has increased scrutiny over some China Evergrande accounts and issued verbal and written warnings to the company to rein in such behavior.

Earlier this year, the stock exchange announced it would increase scrutiny of merger and restructuring deals and impose trading halts on highflying stocks in an attempt to rule out irregularities and curb speculation.

Chinese authorities have also looked into China Evergrande's building of a stake in China Vanke Co., which has been embroiled in a long-running battle against a hostile takeover with another company.

Since August, China Evergrande has raised its holding in China Vanke to 8.285% for a total of 18.8 billion yuan ($2.8 billion), according to a corporate filing Wednesday. China Evergrande said the most recent increase in its stake was "investment behavior."

Evergrande Life Insurance, the life insurer subsidiary of the conglomerate owned by billionaire Xu Jiayin, raised skepticism among investors after it was revealed to have dumped shares this month in at least five stocks, including Zhejiang New Material Co. and Guangdong Meiyan Jixiang Hydropower Co. after snapping up close to 5% shares in each stock. Those amounts are just under the trigger point for disclosure. In China, listed companies are required to disclose to investors when any shareholder raises holdings to 5% or more.

"We have issued query letters to listed firms inquiring motivations behind share holdings by China Evergrande-related accounts, and whether the firms failed to comply with disclosure rules," said the notice.

Already listed in Hong Kong, China Evergrande is seeking to return to the yuan-denominated A-shares market via a reverse merger with Shenzhen Special Economic Zone Real Estate and Properties.

China Evergrande Group surpassed China Vanke as the country's largest developer by sales during the first 10 months this year.

--Yifan Xie contributed to this article.

Write to Yifan Xie at yifan.xie@wsj.com

(END) Dow Jones Newswires

November 11, 2016 15:10 ET (20:10 GMT)

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