Washington ? U.S. officials said Monday that they had learned of credible threats of airline suicide hijackings by terrorists planned for later this summer.

The information was developed in recent interviews with one or more high-level al-Qaida captives and corroborated separately by other means, including electronic intercepts, officials said. They described the possible scenarios as similar to the hijackings of four U.S. airliners on Sept. 11, 2001, that were crashed into the World Trade Center, the Pentagon and a field in western Pennsylvania.

“The U.S. intelligence community has received information related to al-Qaida’s continued interest in using commercial aviation here in the United States and abroad to further their cause,” said Department of Homeland Security spokesman Gordon Johndroe. “The Department of Homeland Security issued an advisory regarding this information over the weekend to the appropriate airline and security personnel.”

Information about the possible attacks began emerging last week, government sources said. It could not be learned Monday which al-Qaida captives had provided the information, but officials said they had taken steps to verify its credibility. “It didn’t just come from one place,” an intelligence official said.

“We are continuing to investigate the credibility of the information,” Johndroe said.

Homeland Security officials said they had no immediate plans to raise the government’s threat index, which mandates stepped-up security by local, state and federal officials throughout the country, but said the threat level was evaluated every day.

The threat level was dropped May 30 to “yellow,” indicating “elevated risk,” after a 10-day stretch at level “orange,” indicating “high risk.” The index was boosted to orange in response to al-Qaida’s May 12 suicide bombings in Riyadh, Saudi Arabia, and an increase in al-Qaida “chatter” gathered through a variety of intelligence methods.

Several high-level al-Qaida operatives have been captured since the Riyadh bombings.

Law enforcement and security officials have been notified of the new information, as have the airlines. Federal intelligence agencies have briefed senior administration officials.

“We routinely provide intelligence information to the private sector, and state and local law enforcement, so that they may be informed and take any necessary precautions,” Johndroe said.