Insurance mergers and acquisitions rarely raise red flags with U.S. national security watchdogs.

China's Fosun International Ltd took that history to heart last year when it paid $1.84 billion for the remaining 80 percent stake of U.S. property and casualty insurer Ironshore Inc that it did not already own.

But in December 2015, one month after Fosun completed the acquisition, it was approached by officials at the Committee on Foreign Investment in the United States (CFIUS), a government panel that scrutinizes deals over national security concerns, according to people familiar with the matter who asked not to be identified because these details are not public.

CFIUS was concerned about how Fosun would operate Ironshore's Wright & Co, a provider of professional liability coverage to U.S. government employees such as law enforcement personnel and national security officials, including the Central Intelligence Agency, according to these sources.

Fosun, Ironshore and CFIUS all declined to comment on the process.

CFIUS operates a voluntary filing system for companies engaged in a deal. Such an instance of the panel approaching companies after they complete a deal is rare.

But the recent U.S. scrutiny of Fosun -- which did not seek CFIUS approval for the Ironshore deal -- is just one example of a new impetus by CFIUS to target what it refers to as "non-notified transactions" -- or deals that did not seek CFIUS approval in advance.

In the last twelve months CFIUS has stepped up its pursuit of these non-filers over concerns that some deals were falling through the cracks, according to sources with direct knowledge of the panel's inner workings. This previously unreported push by CFIUS has the potential to delay some deals and raises the risk of them being thwarted altogether.

While Wright accounted for a tiny fraction of Ironshore's business, the inquiry has forced Fosun to delay its initial public offering of Ironshore, which has been registered with the U.S. Securities and Exchange Commission since June, until CFIUS clears the original acquisition. Fosun will now likely miss a window for IPOs due to the expected market volatility around the Nov. 8 U.S. presidential election, according to the sources.

Chinese companies have been treated with suspicion by CFIUS because of the ties many of them have to the country's communist regime, reflecting the complicated diplomatic and commercial ties between China and the United States.