(Adds details on packages sent to Waters, Holder, context)
WASHINGTON/NEW YORK, Oct 24 (Reuters) - Police intercepted suspected bombs mailed to former U.S. President Barack Obama, former presidential candidate Hillary Clinton and other high-profile Democrats in what New York officials described on Wednesday as an act of terrorism.
With the country deeply polarized, the packages brought a new level of tension to Nov. 6 political contests that will decide whether Democrats can challenge the majorities now held by President Donald Trump's Republicans in Congress.
The CNN bureau in New York also received a device looking like a pipe bomb, leading police to evacuate the building in a busy part of New York City near Central Park.
Eric Holder, who was U.S. attorney general under Obama, and Democratic Representative Maxine Waters were also among those targeted.
The mailed devices had the appearance of pipe bombs, though experts said there was no indication the improvised devices could be detonated remotely.
A similar-looking explosive device was delivered earlier this week to the home of George Soros, a prominent Democratic Party donor.
There was no immediate claim of responsibility.
"This clearly is an act of terror attempting to undermine our free press and leaders of this country through acts of violence," New York Mayor Bill de Blasio told a news conference.
Trump condemned what he called "despicable acts" and vowed to bring those responsible to justice.
Trump, who usually relishes in making partisan attacks on Democrats, also issued a rare call for unity.
"In these times, we have to unify, we have to come together, and send one very clear, strong, unmistakable message that acts or threats of political violence of any kind have no place in the United States of America," Trump said at the White House.
"We're extremely angry, upset and unhappy about what we witnessed this morning, and we will get to the bottom of it," Trump said.
All of the targets are frequently disparaged by right-wing critics.
Soros is a frequent target of anti-Semitic conspiracy theories, some voiced openly by Trump supporters, that he is part of a secretive effort by elites to control the world.
Alexander Soros, the son of George Soros, said in an opinion piece published by The New York Times that his father had long faced threats over his involvement in politics, "but something changed in 2016" when Trump was elected.
"Before that, the vitriol he faced was largely confined to the extremist fringes, among white supremacists and nationalists who sought to undermine the very foundations of democracy. But with Donald Trump's presidential campaign, things got worse," Alexander Soros wrote.
He placed direct responsibility with those who sent the devices, but added: "I cannot see it divorced from the new normal of political demonization that plagues us today."
The package to Clinton was found late on Tuesday while the one addressed to Obama was recovered early on Wednesday, both during routine off-site mail screenings, the Secret Service said. Obama and Clinton were not at risk, they said.
Officials said the package received by CNN was addressed to former CIA director John Brennan, who appeared on CNN periodically before joining cable news rival MSNBC as a paid contributor.
CNN is a frequent target of Trump, who routinely calls the news media the "enemy of the people" and belittles critical coverage as "fake news."
Brennan has been an outspoken critic of Trump, calling the president's performance during a July joint news conference with Russian President Vladimir Putin in Helsinki "nothing short of treasonous."
The package sent to CNN also contained an envelope of white powder that experts were analyzing, Police Commissioner James O'Neill told the news conference.
In the weeks following the attacks of September 11, 2001, anthrax spores were mailed to news media offices and two U.S. senators, killing five people and infecting 17 others.
The intercepted packages had the return address of U.S. Representative Debbie Wasserman Schultz, a former Democratic Party national chairwoman, media reported.
A suspicious package was found at the building that houses Wasserman Schultz's office, the Broward Sheriff's office said.
CNN said the package was meant for Holder but sent to the wrong address and returned to Wasserman Schultz's office.
Waters said in a statement that her Washington office was the target of "a suspicious package." The package was intercepted at a Maryland mail processing facility, NBC reported.
(Reporting by Makini Brice and Jonathan Allen; Steve Holland, Doina Chiacu, Mark Hosenball and Susan Heavey in Washington, Gina Cherelus and Gabriella Borter in New York; Additional reporting by Subrat Patnaik in Bengaluru; Writing by Susan Heavey and Dan Trotta; Editing by Jeffrey Benkoe and Rosalba O'Brien)