Recent communications between Usama bin Laden (search) and Abu Musab al-Zarqawi (search) indicate that bin Laden has "encouraged Zarqawi and his group to focus on attacks inside the United States," multiple U.S. officials told FOX News on Monday.

The sources would not get into detail about how the communication was made or how it was intercepted by the United States. They also said that there is nothing specific in the message, such as maps or references to particular cities or buildings. Rather, the communication simply encourages a "focus" on attacks inside U.S. borders, sources said.

The Homeland Security Department issued a classified bulletin to officials over the weekend about the intelligence, which spokesman Brian Roehrkasse described as "credible but not specific." The intelligence was obtained over the past several weeks, officials said.

The U.S. has no immediate plans to raise its national alert level, Roehrkasse said. However, the intelligence "reiterates the desire by Al Qaeda and its associates to target the homeland," he said.

Zarqawi, the leader of Al Qaeda (search) in Iraq and believed to be the inspiration of the ongoing bombings, beheadings and attacks on Iraqi and American forces, pledged his alliance to bin Laden last year and changed the name of his group in Iraq to reflect his ties to Al Qaeda. Iraqi officials said they expect to take Zarqawi soon; they recently nabbed a key associate and driver of the Jordanian-born terror leader.

U.S. officials say Zarqawi has "his hands full" trying to stay out of U.S. or Iraqi custody in Iraq and they question whether Zarqawi's group would have the ability to pull off an attack inside America. Also, officials are wondering aloud what this means about Al Qaeda and whether if the group is reaching out to its central leader because they are under significant pressure.

Another administration official with access to the Homeland Security Department's bulletin said the intelligence indicates that Al Qaeda has continued to encourage al-Zarqawi, who was born in Jordan, to get involved in terrorist actions against Americans outside of Iraq, including in the United States.

"The intelligence continues to be analyzed by the intelligence community and all appropriate information will be passed on to homeland security partners," Roehrkasse said. "The department has no plans at this time to raise the threat level based on this nonspecific information."

FOX News' Bret Baier, Nick Simeone and The Associated Press contributed to this report.