The latest statement by Al-Qaeda chief Osama bin Laden contains language considered a valid indicator of an upcoming attack, the IntelCenter US monitoring group said on Friday.
In an audio message posted on jihadist Internet forums on Friday, bin Laden called on European countries to end their alliance with the United States and withdraw their forces from Afghanistan, monitoring organisations said.
"This indicator when viewed in light of the five Abu Talha videos this year, three of which have been released in the last eight days and their focus on the upcoming elections in Germany, significantly raises the threat level even further," IntelCenter said.
"There is currently a very high threat of an attack occurring in Germany or against German interests in the immediate period and extending for at least the next four weeks. A single or multiple-stage attack may occur before, during or after the elections against a German target or targets," it said.
The audio message was contained in a near-five minute video from the As-Sahab media branch of Al-Qaeda showing only a still image of bin Laden, SITE Intelligence Group said, noting that English- and German-language subtitled versions of the video were posted.
The release of the statement comes two days before Sunday's German general election.
IntelCenter and SITE both reported Bin Laden as saying: "An intelligent man doesn't waste his money and sons for a gang of criminals in Washington, and it is a shameful thing for a person to be in a coalition whose supreme commander has no regard for human life and intentionally bombs villagers from the air."
Europeans would understand attacks in London and Madrid if they saw what the United States did in Afghanistan, the Al-Qaeda chief said in the message.
The message's authenticity cannot be independently verified.
"Were you to see what your American ally and his helpers did in northern Afghanistan, and how they packed thousands of Taliban into freight containers like sardines and locked them inside until they died or were thrown into the river, you would understand the causes of the bloody events in Madrid and London," the video subtitles quoted bin Laden as saying.
Bombings on trains in Madrid in March 2004 killed 191 people. Bombings on London transport in July 2005 killed 56 people, including the four suicide bombers.
"If today Europe is suffering the travails of the economic crisis, and the heart of Europe is no longer number one in world exports, and America is reeling from the haemorrhage caused by the economic war, then how do think you will fare after America pulls out?" bin Laden said, according to the video.
He threatened that Al-Qaeda would retaliate "from the oppressor on behalf of the oppressed," the subtitles showed.
In the past week three German-language videos by Al-Qaeda operative Abu Talha al-Almani have surfaced in what the German government said on Friday marks an "abstract threat" against the country.
Last week Abu Talha warned Germany in a video to change its government in the election and withdraw its 4,200 troops from Afghanistan or face being attacked at home.
Friday's audio message is the second this month purportedly by bin Laden.
On September 14, As-Sahab issued a video containing an audio statement by bin Laden in which he said Obama is "powerless" to halt the wars in Afghanistan and Iraq and must rethink his policy on Israel.
Bin Laden said that among "some other injustices," US support for Israel motivated Al-Qaeda to launch the September 11 attacks, IntelCenter reported.
Bin Laden has a 50-million-dollar bounty on his head and has been in hiding for the past eight years.
Intelligence officials, military analysts and other experts have long believed he is holed up along the remote mountainous border between Pakistan and Afghanistan.