New York ? Financial industry workers returned to work with determination and little trepidation Monday following a government warning that terrorists may be planning to strike “iconic” financial institutions.

Streets were closed around the New York Stock Exchange, Citigroup Center in midtown Manhattan, Prudential Financial Inc.’s headquarters in Newark, N.J., and the International Monetary Fund and World Bank in Washington. All were identified by authorities Sunday as terrorism targets. Police wearing flak vests and armed with automatic weapons kept a wary eye on the crowds of employees waiting to get through increased security to get into the buildings.

“Just look around,” said Arturo Ramirez, a maintenance worker at Citigroup, as he pointed to a pair of armed and armored police officers. “Now that these buildings have been named in the media and all the police are here, who’s going to try anything? I feel safer now than I did before.”

To show their confidence in the city’s security, Mayor Michael Bloomberg, Sen. Charles Schumer and Gov. George Pataki rang the opening bell at the stock exchange.

“I would use the word defiant to describe these guys,” Pataki said as he toured the floor of the exchange, shaking hands with traders. “It makes us proud to see all these people here with American flags on their jackets going about their work.”

None of the targeted businesses reported unusual numbers of absentees Monday, and many of the people working at the buildings, when asked about their feelings regarding the terrorist threat, just shrugged, though many said they received calls from concerned friends and family about the threat.

Armed policemen stand guard outside the New York Stock Exchange. Monday, the United States raised the terror threat level from elevated to high for financial institutions.