The Latest on senior U.S. officials' testimony to Congress on terror threats (all times local):

10:40 a.m.

Homeland Security Secretary Jeh (jay) Johnson says terrorist threats have evolved. He says they include individuals living in the U.S. who are "self-radicalized" to attack their own country.

Johnson told a Senate committee on Tuesday that some U.S. residents and citizens are inspired by terrorist propaganda on the internet. Johnson says some attacks are "terrorist-enabled," in which established groups provide general guidance, such as potential targets, often in online conversations with terrorists overseas.

Johnson says another category of attacks is "terrorist-validated," which a terror group such as the so-called Islamic State claims responsibility for an attack after the fact.

Johnson and other officials are testifying before the Senate Homeland Security and Government Affairs Committee on security threats 15 years after the Sept. 11, 2001 attacks on New York and Washington.

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9:30 a.m.

In prepared testimony before a Senate committee, Homeland Security Secretary Jeh (jay) Johnson says air strikes and special operations against the Islamic State group have led to the deaths of a number of its leaders. He says the group has lost nearly half the populated areas it once controlled in Iraq and thousands of square miles in Syria.

At the same time, Johnson says, the group has "increased its plotting on targets outside of Iraq and Syria and continues to encourage attacks in the United States."

Johnson, FBI Director James Comey and Nicholas Rasmussen, director of the National Counterterrorism Center, are set to testify as the Senate Homeland Security and Government Affairs Committee looks at security threats 15 years after 9/11.