Mainland regulators have told domestic banks to stop lending to United States financial institutions in the interbank market in a bid to prevent possible losses during the financial crisis, industry sources said yesterday. The ban from the China Banking Regulatory Commission (CBRC) applied to interbank lending of all currencies to US banks but not to banks from other countries, a source said. The CBRC was not available for comment yesterday. The decree appears to be Beijing's first attempt to erect defences against the deepening US financial meltdown after the mainland's major lenders reported billions of US dollars in exposure to the credit crisis. Lending transactions on the mainland interbank market totalled 10.65 trillion yuan (HK$12.17 trillion) last year, according to the People's Bank of China. In the first eight months of this year, transactions totalled 10.11 trillion yuan, up 104 per cent from a year earlier. At the end of last year, the mainland interbank market had 717 members, including banks, securities companies and trust companies. Another banking source said the CBRC issued the ban after obtaining data about the exposure of mainland banks to bonds issued by bankrupt Lehman Brothers Holdings. Top officials said they were keeping a close watch on the crisis and warned mainland financial institutions to be cautious in their daily business and overseas expansion. 'The international transaction volume of Chinese banks is not big. Those concerning subprime loans are probably lower than US$10 billion,' deputy central bank governor Ma Delun wrote this week in the China Business Post, a PBOC-affiliated newspaper. But the deteriorating situation in the US has shocked top officials. Mr Ma said that among the unexpected developments was the effect the crisis was having on normal assets, not just problematic assets; its impact on the whole credit market, not just single products; and its effect on Europe and other nations, not only the US. The exposure of seven listed mainland banks to bonds related to Lehman Brothers totalled US$721 million. Mainland banks had US$9.8 billion in exposure to US subprime loans at the end of last year and US$25 billion to Fannie Mae and Freddie Mac by June 30.