BERLIN (Reuters) - Germany should brace for further attacks given growing numbers of potential Islamist militants, top security officials warned on Tuesday, vowing to step up efforts to prosecute, convict and deport suspects.

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Germany was hit by five Islamist attacks in 2016, including a December attack on a Berlin Christmas market that killed 12 people, while an additional seven attacks failed or were thwarted, Hans-Georg Maassen, president of Germany’s BfV domestic intelligence agency, told reporters.

“We must expect further attacks by individuals or terror groups,” Maassen said, citing growing evidence and over 1,000 expressions of concern from the general public about growing risks.

“Islamist terrorism is the biggest challenge facing the BfV and we see it as one of the biggest threats facing the internal security of Germany,” he said.

The agency’s annual report for 2016 said there were 24,400 Islamists in Germany, including around 9,700 Salafists, and the number of Salafists had increased to 10,100 this year. The total also includes some 10,000 members of the Turkish Islamist Milliu Gorus movement, the report showed.

The total number of suspected Islamists marks a drop from the year earlier, but the report said that did not mean the threat had diminished.

“In fact the opposite is the case,” the report said, citing a shift toward “a more violence-prone and terrorist spectrum ...”

The report said hundreds of “jihadists” had entered the country among the over one million migrants who had come into Germany over the past two years.

Altogether, security officials were keeping tabs on some 680 potential Islamist threats, most of whom were influenced by Salafist ideology, Interior Minister Thomas de Maiziere said.

He said Germany had dramatically stepped up its efforts to combat Islamistic militancy, with a record number of arrests, prosecutions and deportations seen over the past year.

Maassen said an estimated 930 people had left Germany to fight with Islamic State in Syria or Iraq, of whom about 20 percent were women. An estimated 145 of the total people had since died, he said.