Berlin, Germany (CNN) -- Concrete evidence has emerged of a possible attack planned in Germany later this month and persistent efforts by Islamists to attack the federal republic, Interior Minister Thomas de Maiziere said Wednesday.

There is "reason for concern but no reason for hysteria," said de Maiziere, adding that the information is coming from German and foreign intelligence.

De Maiziere told reporters that since mid-year, security officials "have logged increased indications, according to which the terror organization al Qaeda is believed to be planning to carry out attacks" in the United States and Europe, including Germany.

"Security authorities are considering three different threat scenarios by international terrorists. Security authorities have been pursuing these indications for weeks with the highest intensity and proper sensitivity -- in closest cooperation with our international partners.

"Now further insights and facts relevant to danger have added themselves to these established insights" and spurred a hike in the country's threat level because of what is termed a "new situation." The level is now the same as it was during Germany's September 2009 federal elections.

Last month, the United States issued a general travel alert for Americans in Europe amid concerns that al Qaeda or related groups might be planning attacks similar to the 2008 massacre in the Indian city of Mumbai.

A group of jihadists from the German city of Hamburg was alleged to be at the heart of the purported plot, European intelligence officials said.

Western intelligence officials say they learned about the alleged plot after Ahmed Sidiqi, a German citizen of Afghan descent, was arrested in Afghanistan in July and taken to the U.S. air base at Bagram for questioning.

"You are aware that the federal security authorities have been presuming a stronger threat situation from international terror for a considerable time," de Maiziere said. "In spring 2009 and in the time thereafter, there were detailed indications of possible attacks in the U.S.A., in Europe and in Germany as well."

De Maiziere mentioned the attempted strikes on international air freight carriers at the end of last month. Al Qaeda in the Arabian Peninsula claimed responsibility for those plans.

After the Yemen developments, he said a clue from a foreign partner emerged about "an alleged attack plan" to be carried out at the end of November.

"Our own latest investigations by the Federal Criminal Office in conjunction with persons from the Islamist realm confirm independently and additionally the continued endeavors of Islamist groups towards plans to attack the Federal Republic of Germany," he said.