By Sarah Marsh

BERLIN (Reuters) - The man arrested after a Spanish tourist was stabbed at Berlin's Holocaust memorial on Friday was a 19-year-old Syrian refugee, Berlin prosecutors said, a day before a national election in which concerns over migration are expected to boost the far-right AfD party.

Motivated by the Middle Eastern conflict, the suspect appears to have been planning to kill Jews for several weeks which is why he chose this location, the prosecutors said in a statement.

Police arrested the suspect, whose hands and trousers were smeared with blood, shortly after the stabbing on Friday evening.

The 30-year old Spanish tourist underwent emergency surgery after sustaining injuries to his neck and was placed in an induced coma, the statement said, adding that he is no longer in a life-threatening condition.

Campaigning for Sunday's election has been marred by a series of high-profile attacks in which the suspects are from migrant backgrounds, shifting the focus away from Germany's ailing economy and boosting support for the Alternative for Germany, which is on track to secure second place.

A stabbing in which two were killed including a toddler was blamed on an Afghan immigrant, prompting the conservative CDU/CSU bloc to break a taboo on cooperating with the far-right to push a motion cracking down on migration through parliament with support of the AfD.

In December, a Saudi man who had lived in Germany for years, and whose social media posts indicated he sympathised with the AfD, rammed a car into a Christmas market, killing six and injuring hundreds.

The Holocaust memorial, one of the German capital's most sacred sites, commemorates the 6 million Jews murdered by Adolf Hitler's Nazis during World War Two, one of the darkest episodes in human history and a continuing focus of German historical atonement.

(Reporting by Sarah Marsh; additional reporting by Graham Keeley in Madrid; Editing by Kirsten Donovan)