CHICAGO — Tensions were increasing here on Saturday, the eve of a NATO summit meeting, after three men were accused of planning attacks on President Obama’s re-election campaign headquarters, the house of Mayor Rahm Emanuel, police stations and financial institutions in downtown Chicago, according to prosecutors.

The men, who were among thousands of people from out of town who traveled to Chicago for a weekend of NATO-related protests, were charged with criminal acts relating to terrorism, conspiracy to commit terrorism, and possession of explosives. Bond for the three men — Jared Chase, 27, of Keene, N.H.; Brent Betterly, 24, of Oakland Park, Fla.; and Brian Jacob Church, 22, of Fort Lauderdale, Fla. — was set at $1.5 million each. The state’s attorney, Anita Alvarez, said that this was the first time she knew of that defendants had been charged under the state’s antiterrorism statute. She declined to comment on possible federal charges.

During a news conference on Saturday, officials said that there was no imminent threat to the city, describing the defendants as self-identifying anarchists.