National Intelligence Director James Clapper gives his opening statement on behalf of the top intelligence officials before the Senate Intelligence Committee on Tuesday. Clapper discussed worldwide threats to United States, including North Korea, Iran and Syria. (Kris Anne Bonifacio/Medill)

WASHINGTON — One day after North Korea threatened a preemptive nuclear strike against the U.S., , intelligence officials testified at a Senate panel Tuesday that it is very possible for the “belligerent” nation to attack its neighbors to the south.

In a rare hearing open to the public, Director of National Intelligence James Clapper listed for the Senate Intelligence Committee the top worldwide threats to the United States. The increasing tensions between North and South Korea were at the top of the list, particularly after North Korean leader Kim Jong-Un’s announcement Monday that the 1953 Korean War armistice was nullified.

“The rhetoric, while it is propaganda-laced, is an indicator of their attitude and perhaps their intent,” Clapper said. “I am very concerned about what they might do.

In his prepared statement, Clapper said that North Korea is using nuclear weapons for international recognition and “coercive diplomacy.”

“Although we assess with low confidence that the North would only attempt to use nuclear weapons against U.S. forces or allies to preserve the Kim regime” he said, “we do not know what would constitute, from the North’s perspective, crossing that threshold.”

Clapper appeared in front of the Senate panel with top officials from intelligence agencies, including FBI Director Robert Mueller and CIA Director John Brennan, who appeared before that same committee just two weeks ago for his confirmation hearing.

Issues raised during Brennan’s confirmation resurfaced Tuesday, especially when Sen. John Rockefeller, D-W.Va., expressed frustration over roadblocks in intelligence communication with Congress.

“It’s a terrible situation,” Rockefeller said. “What happened over the last couple of weeks is a threat, is a threat to trust between us and you, us towards you and you towards us.”

Had it not been for Brennan’s nomination, the White House would not have shared the documents that provided the legal basis for President Barack Obama’s authority to kill U.S. citizens who are al-Qaida members, Rockefeller said.

Rockefeller said he was frustrated at the lack of cooperation by intelligence agencies with Congress, making it difficult to exercise oversight. He said perhaps the Senate should pass a bill that makes it mandatory for the intelligence community to share information with Congress, much like it passed a bill after the Sept. 11 attacks that improved communication between the FBI and CIA.

For their part, the intelligence heads also seemed frustrated with Congress for not preventing the across-the-board automatic spending cuts, known as the sequester, that began March 1. Clapper said the intelligence community seems to be subject to a more “onerous set of rules” than the Defense Department.

“Unlike more directly observable sequestration impacts like shorter hours in public parks and longer security lines at airports, the degradation to intelligence will be insidious,” he said in his opening remarks. “It will be gradual and almost invisible, unless and until of course, we have an intelligence failure.”

The sequester has cut about $4 billion from intelligence budgets, Clapper said. Intelligence Committee Chairwoman Dianne Feinstein, D-Calif., said she had proposed an amendment that would have allowed intelligence officials more flexibility with which programs to cut under sequester.

“All we’re asking for is the latitude on how to take them to minimize the damage,” Clapper said.

But Sen. Barbara Mikulski, D-Md., who chairs the Senate Appropriations Committee, said she was unable to include intelligence under the continuing resolution she proposed this week.

The House passed the continuing resolution that provided for flexibility in defense spending, and Mikulski said she and Alabama Sen. Richard Shelby, the top Republican on the Appropriations Committee, worked to add amendments for other departments. Intelligence agencies were not included, she said, because the House warned that they would be “poison pills.”

Clapper also addressed other threats, including Syria’s ongoing civil war, threat of Iran’s nuclear capabilities and the growing offshoots of al-Qaida in North Africa, but reserved more detailed information for the closed hearing that followed the open hearing.

Josh Solomon contributed reporting on this story.