WASHINGTON (Reuters) - Democratic and Republican U.S. senators announced legislation on Thursday that would impose sanctions over an alleged plot by Iranian intelligence agents to kidnap Iranian-born U.S. journalist Masih Alinejad.

       Democrat Ben Cardin and Republican Pat Toomey said their legislation would seek to hold Iran accountable for the plot and prevent any further attempted kidnappings on U.S. soil by imposing mandatory sanctions on those involved and authorizing secondary sanctions on banks doing business with them.

       U.S. prosecutors charged four Iranian operatives in July with plotting to kidnap Alinejad, a journalist who was critical of Tehran. Iran has called the allegation "baseless."

       "If you dare to attempt to come to our nation and kidnap an American citizen, there will be dire consequences," Cardin told a news conference with Toomey and Alinejad, who said she came out of hiding for the event at the U.S. Capitol.

       The U.S. Treasury department said in September it had sanctioned the four Iranian intelligence operatives behind the failed plot.

       The bill's path to becoming law was not immediately clear, but Cardin and Toomey said they would do everything possible to see it was passed and sent to the White House for President Joe Biden to sign into law.

       "I am cautiously optimistic," Toomey said.

       (Reporting by Patricia Zengerle)