U.S. President Barack Obama said on Friday that initial tests on two packages found on U.S.- bound cargo planes confirmed they "apparently contain explosive material," and that investigators had discovered a "credible terrorist threat" against the country.

U.S. President Barack Obama makes a statement to the press at the White House in Washington D.C., capital of the United States, Oct. 29, 2010. Obama said on Friday that initial tests on two packages found on cargo planes bound for the U.S. confirmed they "apparently contain explosive material," and investigators had discovered a "credible terrorist threat" against the U.S.. [Zhang Jun/Xinhua]

"An initial examination of those packages has determined that they do apparently contain explosive material," Obama said in a statement at the White House.

Officials had previously said one of the suspicious packages, found in East Midlands of Britain, contained a "manipulated" toner cartridge but later tested negative for explosive material.

Authorities are suspecting that al-Qaeda's Yemeni affiliate was behind the security scare, in which two suspicious packages were found on Thursday night on cargo planes originating from Yemen and destined for the United States.

"We know that al-Qaeda in the Arabian peninsula, the terrorist group based in Yemen, continues to plan attacks against our homeland, our citizens, and our friends and allies," said Obama. " Going forward, we will continue to strengthen our cooperation with the Yemeni government to disrupt the plotting and to destroy the al-Qaeda affiliate."

The al-Qaeda affiliate in Yemen, which was designated by the U. S. State Department as a terrorist organization, was responsible for the failed bombing attack on a U.S.-bound airliner on Christmas Day last year.

Obama did not directly label al-Qaeda as the plotter for the latest incidents, as investigations are still under way.

He reminded the American people of "the necessity of remaining vigilant against terrorism."

The White House said earlier on Friday that Obama was briefed on Thursday night about the possible terrorist threat associated with those suspicious parcels, and the president has directed his security team and law enforcement agencies to "take steps to ensure the safety and security of the American people."