WASHINGTON—Two senior Senate Democrats have asked a number of large banks to turn over information about accounts and assets controlled by a group of Russian elites who have been designated by the U.S. Treasury Department for possible sanctions.

In a letter to eight banks, Sens. Jeanne Shaheen (D, N.H.) and Sheldon Whitehouse (D, R.I.) asked the financial entities for details about accounts, assets or services the institutions were providing to any of the 96 Russian oligarchs identified by the Treasury Department in January as having ties to the government of Russian President Vladimir Putin.

The letter was sent last week but reviewed by The Wall Street Journal on Tuesday. The two Democrats said they had received acknowledgment of their letter from three banks, which are reviewing it.

Three of the banks—Bank of America Corp., JPMorgan Chase & Co. and Citigroup Inc. —are U.S.-based. The other five— Barclays PLC, Deutsche Bank AG , UBS Group AG, HSBC Holdings PLC ADR and Credit Suisse Group AG —are headquartered abroad but in many cases have a significant presence in the U.S.

A spokesman for JPMorgan said the bank had received the letter and is reviewing it. Deutsche Bank declined to comment. The other banks didn’t immediately respond to requests for comment Tuesday night.