(Bloomberg) —The White House will hold a briefing for senators with its “four principals” on North Korea as the administration considers its options for dealing with saber-rattling from Pyongyang.

Secretary of State Rex Tillerson, Defense Secretary Jim Mattis, Director of National Intelligence Dan Coats and Joseph Dunford, chairman of the Joint Chiefs of Staff, will attend the meeting planned for April 26, the White House said in an advance schedule.

Over the weekend, North Korea detained a U.S. citizen who’d been teaching at a university there as he was leaving the country, according to media reports that cited officials with the Swedish embassy in Pyongyang. Three Americans are now being held in the isolated nation.

“We are aware of reports that a U.S. citizen was detained in North Korea,” a State Department official said in a brief statement. “In cases where U.S. citizens are reported to be detained in North Korea, we work with the Swedish Embassy, which serves as the United States’ Protecting Power in North Korea. Due to privacy considerations, we have no further comment.”

Trump’s schedule was amended to add calls with Japanese Prime Minister Shinzo Abe and Chinese President Xi Jinping Sunday night. The topic wsn’t announced. Trump said on April 20 he was confident China is working “very hard” to defuse tensions with North Korea.

North Korea on Sunday said it was ready to sink a U.S. aircraft carrier to show its military strength, Reuters reported, citing North Korea’s state-run Rodung Sinmun. The USS Carl Vinson is heading to the Western Pacific to conduct drills with two Japanese destroyers amid heightened tensions over the North’s missile tests.

Vice President Mike Pence said during a visit to Sydney this weekend that all options are “on the table” for the U.S. Pence is winding up a 10-day trip to Asia and the Pacific in which he has regularly criticized North Korea.

Homeland Security Secretary John Kelly said on Sunday’s “Face the Nation” on CBS that while North Korea poses mostly a cyber threat to the U.S. today, that could change.

“The instant they get a missile that can reach the United States, and they have a weaponized atomic device, nuclear device on it, we’re at grave risk as a nation,” he said.