BERLIN - German authorities suspect that an Islamist who once lived in Germany carried out a car bombing on a hotel in Mogadishu on Sunday that killed at least 13 people, security sources told Reuters on Tuesday.The sources said the man, Abdirazak Bouh, was born in Libya and had both Somali and Libyan passports. Born in 1985, he had lived for some time in Bonn, where security officials say a strong Salafist movement is active.He was barred from leaving Germany in 2009 because he was suspected of wanting to join Islamists fighting abroad, said the sources. However, in 2012, he succeeded in travelling to Egypt and then on to Somalia.The sources confirmed a report by Die Welt daily that said he had joined the al Shabaab group, which said it was behind the blast on the Jazeera hotel in Mogadishu on Sunday.The group frequently stages bomb and gun attacks in the capital aiming to topple Somalia's Western-backed government. It also wants to impose its strict version of Islam on Somalia, which is trying to rebuild after two decades of conflict and chaos.Germany's BfV domestic intelligence agency has warned about a rising number of Islamist militants in Germany travelling to Syria, Iraq and other countries to fight.Der Spiegel Online reported that the BfV now thinks some 720 people have travelled from Germany to Syria or Iraq to join jihadist forces such as Islamic State. They are also worried about the number of those returning to Germany.