Bombings in New York and New Jersey — and a stabbing attack in Minnesota the same day — underscore that homegrown attacks inspired by violent extremists are as much a threat to the United States as those directed by terrorists, the nation’s Homeland Security chief says.

While all attacks are difficult to detect and prevent, Homeland Security Secretary Jeh Johnson said the United States and its allies continue to “take the fight militarily to terrorist organizations overseas” 15 years after the Sept. 11, 2001, attacks on New York and Washington.

In prepared testimony before a Senate committee Tuesday, Johnson said air strikes and special operations against the so-called Islamic State terror group have led to the deaths of a number of its leaders. While it remains a threat, the Islamic State has lost nearly half the populated areas it once controlled in Iraq and thousands of square miles in Syria, Johnson said.

At the same time it loses territory, the group has “increased its plotting on targets outside of Iraq and Syria and continues to encourage attacks in the United States,” Johnson said.

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

The panel’s chairman, Sen. Ron Johnson said the threat of “militant Islamic terrorist attacks to the United States remains significant,” citing the Sept. 17 attacks in the New York region and Minnesota, as well as deadly attacks in San Bernardino, Calif., and Orlando.

“In all, Islamic extremist terrorist have killed 63 people on U.S. soil since our committee last held its annual hearing to consider threats to the homeland,” Ron Johnson, R-Wis., said in a prepared statement.

Two years after President Barack Obama stated a goal of defeating the Islamic State, also known as ISIS, “we have made little progress,” said Johnson, who is not related to the Homeland Security chief.

Ahmad Khan Rahami, the main suspect in the New York bombing, faces federal terrorism charges after a shootout with police.

Prosecutors say Rahami, 28, planned the explosions for months as he bought components for his bombs online and set off a backyard blast. They say he wrote a journal that praised Osama bin Laden and other Muslim extremists, fumed about what he saw as the U.S. government’s killing of Muslim holy warriors and declared “death to your oppression.”

While Republican presidential nominee Donald Trump has suggested a temporary ban on Muslim immigrants, Jeh Johnson said the U.S. should focus on “building bridges to diverse communities” to defend the homeland.

Lawmakers also may focus on police shootings in Tulsa, Okla., and Charlotte, N.C., as well as Hillary Clinton’s use of a private email server while she was secretary of state.

Republicans have assailed Comey’s decision not to prosecute Clinton, now the Democratic nominee for president. Several have demanded the Justice Department investigate whether Clinton lied during testimony last year on the deadly 2012 attacks in Benghazi, Libya. Democrats call the claims partisan and intended to hurt Clinton’s candidacy.

(AP)