Crisil on Wednesday put the rating of debt instruments of 27 Indian arms of global banking groups, including Citi and Standard Chartered Bank, "under surveillance" due to the global credit market crunch and turmoil.

"In recent months, there has been considerable uncertainty in the global financial markets over the fallout of the sub-prime episode and credit market crunch. The ratings of global financial institutions have been much less stable than in the past, with several rating downgrades in the sector," Crisil said in a statement.

The agency will keep credit ratings under continuous surveillance. "The examination will cover several aspects, including standalone profiles of the Indian subsidiaries, our assessment of the strength and quality of parent support, and translation of global ratings to the Crisil scale," Crisil Ratings Senior Director Raman Uberoi said.

Crisil, the Indian subsidiary of Standard & Poor's, said these ratings factored in support being made available from the respective parents. Therefore, these arms were linked to the ratings of the global parents.

In this backdrop, Crisil is re-assessing the strength, quality, and extent of support that will be available to the Indian subsidiaries.

However, the agency did not provide any specific timeframe for this exercise and said results would be communicated to the market shortly.

Almost all the instruments enjoy high-safety, investment-grade ratings. "Our exercise is more of a proactive step," Crisil Director S Venkataraman said.