The four European banks, the UBS and Credit Suisse banks of Switzerland, ABN Amro of the Netherlands, and HSBC, based in London, have made varying levels of disclosure about the limits on their activities in Iran in the past six months.

Almost all large European banks have branches or bureaus in the United States, units that are subject to American laws.

The newspaper quoted unidentified U.S. officials as saying that the U.S. had informed its European allies about the new pressure exerted on the banks, and indeed had asked these countries to join the effort.

At the same time, the Americans have not publicized the new pressure, partly out of concern it could complicate efforts by European negotiators, who were still talking with Iran about a package of incentives to suspend uranium enrichment.

Besides, some outside political and economic experts were quoted as saying that it is unlikely to do much damage considering Iran is one of OPEC's leading producers and is earning hundreds of millions of dollars with daily windfall profits from the 70 U.S.-dollars-a-barrel cost of petroleum.

The American prodding has not yet resulted in any fines or other punishment. But UBS and ABN Amro are no strangers to the sting of American financial penalties for dealing with countries that the U.S. has wanted to isolate.

UBS was fined 100 million dollars by the Federal Reserve two years ago for the unauthorized movement of dollars to Iran and other countries like Libya and Yugoslavia, which were subject to American trade sanctions at the time.

Last December, ABN Amro was fined 80 million dollars for failure to comply with regulations against money laundering and with economic sanctions against Libya and Iran from 1997 to 2004.

UBS now says it will no longer do direct business with any individuals, businesses or banks in Iran. UBS also says it will not finance exports or imports for any corporate clients in Iran. But the bank has said that it would not stop doing business with clients who use other means to transact business there.

ABN Amro also says it has minimized its activities in Iran, the New York Times said.