Chinese insurer Ping An Insurance Group believes HSBC has overstated the challenges and difficulties of spinning off the bank, said a source with direct knowledge of the thinking of the bank's biggest shareholder.

The bank came under pressure from Ping An in April to explore options including spinning off its mainstay Asia business to increase shareholder returns.

Details of Ping An's internal discussions come after HSBC on Aug.1 pushed back on the Chinese investor's proposals while reporting its half-year earnings.

HSBC said a break-up would mean a potential long-term hit to the bank's credit rating, tax bill and operating costs, and bring immediate risks in executing any spinoff or merger.

Ping An declined to comment, while a spokesperson for HSBC said the bank had nothing to add to comments made by its executives last week.

The detailed rebuttal as described by the source with knowledge of Ping An's thinking represents the investor's most detailed pushback yet of HSBC's strategy, and signals Ping An's intention to continue the dispute.

While activist investors sometimes acquire a stake in a big bank and confront management on how it is run, it is unusual for a Chinese entity such as Ping An, whose top shareholders include state-backed entities, to take such a proactive stance.

Ping An believes a spin-off would generate an additional $25-$35 billion in market value and release over $8 billion in capital, said the source, citing "external" analysis. The source declined to be identified due to the sensitivity of the matter.

Responding to HSBC's argument that spinning off its Asian business will hit global synergies, the source said HSBC would remain a major shareholder of the Asian unit after the separation and both parties could enter into cooperation agreements.

The spat between HSBC and Ping An shows the challenges facing the UK lender, as it attempts to navigate geopolitical tensions between the U.S., Britain and China amid criticism from lawmakers in the West over the bank's activities in Hong Kong.

HSBC Chief Executive Noel Quinn said on Aug.1 the bank's dialogue with Ping An "has been purely around commercial issues", with no political aspect.