Federal authorities are advising police and law enforcement partners across the country that a terrorism plot uncovered in Australia — involving Australian citizens who were allegedly recruited to join an al Qaeda-linked group in Somalia — has no connection to a similar trend in the United States and does not indicate any heightened threat to the United States.

In a two-page “note” sent to about 18,000 law enforcement organizations nationwide, the Federal Bureau of Investigation and Department of Homeland Security laid out details of the Australian plot but said there is no indication that similar plots are being planned inside the United States.

Hours before dawn on Monday, hundreds of Australian police raided as many as 19 locations in and around Melbourne, Australia’s second-largest city. Four men, all in their 20s, were arrested for allegedly planning to storm an Australian military base with automatic weapons — a suicide mission in retaliation for Western involvement in Somalia. The military base they targeted housed “anti-terrorism units” of the Australian army, according to the note.

The four men, Australian citizens of Somali and Lebanese descent, now face terror-related charges.

The note said the men contacted an imam, or mosque leader, “for approval for the attack.” The note did not specify whether that imam was in Australia, Somalia or another country.

“Intelligence notes are routinely sent to law enforcement partners to provide situational awareness and clarification in comparison to [all the] media reports,” said Justice Department spokesman Rich Kolko. “They are not intended for the general public and are intended for our law enforcement and intelligence community partners.”

Australia, the United States and other countries have recently been assisting Somalia’s secular government as it battles the radical group al-Shabaab, which has ties to al Qaeda and was labeled a terrorist organization by the U.S. government last year. The fighting, which intensified in 2006 after Western-backed Ethiopian forces invaded Somalia, has turned Somalia into a state of anarchy. U.S. officials say if al-Shabaab prevails, Somalia could turn into a haven for al Qaeda and other terrorist groups.

The FBI and DHS note acknowledged media reports that “some” of the plotters received weapons training in Somalia. But, the note said, “the U.S. government has no indication that al-Shabaab or [anyone in] Somalia was aware of the plotting.”

A law enforcement source confirmed to Fox News that at least two of the men arrested Monday in Australia traveled to Somalia recently to train with al-Shabaab. And, according to The Australian newspaper, many others — as many as 14 — wanted to follow suit, but travel plans became so complicated that they decided to focus their efforts on attacks inside Australia.

U.S. authorities have been grappling with a similar — but more severe — trend in the United States. For much of the past year the FBI has been looking into how dozens of young men from the Minneapolis area and elsewhere were recruited to train and possibly fight alongside al-Shabaab in Somalia.

A grand jury in Minneapolis has been investigating the case for several months, and an indictment charging two Minneapolis natives with providing material support to a terrorist organization has already been unsealed. Both men have pleaded guilty and are cooperating with authorities.

A source told Fox News in March that “several” of the American recruits had returned to the United States, but counterterrorism officials have long insisted that such recruits are not planning any domestic attacks.

“Let me stress we don’t have a body of reporting that indicates U.S. persons, who have traveled to Somalia, are planning to execute attacks in the United States,” Andrew Liepman, the deputy director for intelligence of the National Counterterrorism Center, told lawmakers at a Senate hearing on the issue in March. “But we do worry that there is the potential that these individuals could be indoctrinated by Al Qaeda while they’re in Somalia and then returned to the United States with the intention to conduct attacks. They would in fact provide Al Qaeda with trained extremists inside the United States.”

At a briefing with reporters in late June, Secretary of Homeland Security Janet Napolitano expressed a similar assessment of the threat.

“[The recruits'] primary focus obviously is not on the homeland, it’s abroad,” she said. “But any time you have people who are being trained in terrorist-type activities, that’s something that needs to be monitored.”

According to a DHS spokesman, Napolitano’s assessment of the threat facing the United States still holds true. The note issued to law enforcement agencies reflects that.