DENVER — Lawmakers close to Barack Obama remain confident in his security after federal authorities said there is no credible threat to assassinate him.

Officials with both the Democratic convention and the Obama campaign say they have no plans to make any changes to Obama’s planned speech at an open-air football field to accept the presidential nomination on Thursday.

Invesco Field, home to the Denver Broncos, seats 75,000 and lies along an interstate highway, which will be closed for the four hours of Obama’s acceptance.

“The speech will continue as scheduled and we are not commenting on security,” said Nick Shapiro, a spokesman for the Obama campaign, in an e-mail.

Convention delegates were stunned Monday night to hear reports about the arrests of several people in connection with an alleged plot to assassinate Obama. An investigation into the arrests is continuing, but authorities emphasized Tuesday there was no threat to Obama or the people of Colorado.

“We’re absolutely confident there is no credible threat to the candidate, the Democratic National Convention, or the people of Colorado,” said Troy A. Eid, U.S. attorney for Colorado, in a statement.

The Associated Press reported that three men arrested face only gun charges, and that the three men and a woman arrested are not expected to be charged with any national security-related crimes.

A spokesman for the Secret Service expressed confidence in the security for the address.

“We had already put together a very comprehensive, measured and layered security plan for Invesco Field,” said spokesman Malcom Wiley. “So the things that were alleged to have happened in the last couple of days wouldn’t alter our plans.”

Rep. Bennie Thompson (D-Miss.), chairman of the House Homeland Security Committee, said members of his panel received a top-secret briefing from Secret Service officials before the August recess on their preparations concerning security for the presidential candidates.