FRANKFURT (Reuters) - German police said on Thursday they had thwarted a planned Islamist attack, detaining a couple with suspected Salafist militant links, and cancelled a Frankfurt May Day cycle race after they had been seen along the route.

Police stand in front of a home in the courtyard of a building where suspected Salafist Islamist extremists are beleived to live, in Oberursel near Frankfurt, Germany April 30, 2015. REUTERS/Ralph Orlowski

Public prosecutor Albrecht Schreiber said a search of their home had turned up an automatic assault weapon, 100 rounds of live ammunition, chemicals commonly used in preparing home-made bombs and a canister full of petrol.

“Investigations by the police indicate that we have been able to prevent a terrorist attack,” Peter Beuth, the interior minister of Hesse, told reporters. “This incident shows that we must all remain very alert.”

The 35-year-old man had dual Turkish-German citizenship and a criminal record, said Hesse police chief Stefan Mueller. His wife was Turkish and two young children found in their home by police were being cared for by social services.

Police decided to detain the man after he was seen buying large amounts of chemicals which can be used to make explosives - using a false name. He was also seen along the route of Frankfurt’s May 1 cycle race, which attracts thousands of participants and spectators every year.

Police later announced they had cancelled the May Day cycle race as a precaution.

BOSTON MARATHON

Asked if he suspected the pair had been preparing an attack similar to the 2013 Boston Marathon bombing which killed three people and injured more than 260 spectators, Mueller said:

“Clearly since the Boston Marathon these security concerns have been part of the considerations of how to deal with that (danger) before every marathon race in Germany - and that is also valid for cycle races.”

German newspaper Die Welt identified the couple by their first names and initial - Halil and Senay D. - and said they had links to the Salafist scene in Frankfurt and to the al Qaeda network. It did not identify the source for its report.

Salafists advocate a puritanical form of Islam and Germany’s BfV domestic intelligence agency says their numbers are rising, as is the number of potential recruits for Islamic State.

The BfV estimates that 450 people from Germany have travelled to Syria and Iraq to join radical jihadist forces.