Updated at 5:40 p.m. ET
President Obama today confirmed that the suspicious packages discovered by intelligence and law enforcement officials late Thursday night in Dubai and England contained explosive materials.
Mr. Obama confirmed that the packages originated in Yemen and were addressed to Jewish places of worship in Chicago. John Brennan, Assistant to the President for Homeland Security and Counter-terrorism, confirmed they were addressed to synagogues.
Speaking from the White House press briefing room, the president confirmed that he wasof the potential terrorist threat last night and directed the Department of Homeland Security and law enforcement officials to "take whatever steps are necessary" to ensure the safety of U.S. citizens, including additional screening of planes in Newark and Philadelphia -- airports where incoming flights from Yemen were arriving. Officials are also investigating whether there is any connection to al Qaeda in the Arabian Peninsula, which is based in Yemen.
"The events of the past 24 hours underscore the necessity of remaining vigilant against terrorism," Mr. Obama said. "The American people should know the counter-terorrism professionals [investigating the threat are] taking all necesary and prudent steps to ensure our security."
The president is traveling to Philadelphia on Saturday morning and Chicago on Saturday evening as part of a series of campaign stops he is making across the country ahead of the Nov. 2 midterm elections. White House Press Secretary Robert Gibbs said Mr. Obama will not be changing his plans.
"The president was quite clear on this: We are taking this threat very seriously," Gibbs said. That said, he continued, "The president's travel plans both this evening and tomorrow at this point are not expected to change. The president was clear... our counter-terrorism professionals are on the job. The president's not going to change his schedule, and there's no cause for Americans to change their schedules."
Brennan added that election season or not, "there's never a day we relax our guard against al Qaeda."
"The American people should feel particularly good since 9/11 the U.S. government has built up a very capable, robust homeland security system," Brennan said. "We were able to get insight into the fact that there were suspicious packages out there that we had to find."
Brennan said that only two suspicious packages have been found so far, but that "it is very prudent for us to make sure other packages that might be coming from similar routes are looked at very closely."
The FBI, Department of Homeland Security and other domestic agencies are making sure that potential targets of attacks are alerted, Brennan said.
While officials have not confirmed that al Qaeda in the Arabian Peninsula is behind the suspicious packages, Brennan said the group "has been rather open in its venom" toward the United States. The Yemeni government has pledged its full cooperation, Brennan said.
Stephanie Condon is a political reporter for CBSNews.com. You can read more of her posts here. Follow Hotsheet on Facebook and Twitter.