Tourists have been targeted by a knife-wielding would-be robber in the latest in a string of attacks on visitors to Oxford.

The knifeman cycled up to a 54-year-old American woman and her daughter in New College Lane at about 4.30pm on Monday.

He pulled out a knife and demanded they hand over their mobile phones, but they ran away and escaped, leaving him empty-handed.

Just 45 minutes later, the same man cycled up to a 22-year-old Spanish foreign-language student who was taking photographs by the riverbank in Christ Church Meadow.

He held a knife to his face and demanded his camera, but the student turned and fled.

Det Sgt Matt Jarman said: “Both these crimes have seen visitors to our city targeted, and this is something we will not tolerate.

“We will be increasing patrols in these areas and we would like to reassure people we are doing everything in our power to ensure this person is caught as soon as possible.”

The robber was white, aged between 20 and 25, 5ft 8in to 6ft tall, with short dark hair, brown eyes and was riding a dark-coloured mountain bike.

Later that evening, an another attack left a Russian foreign-language student needing four staples to a head wound.

The 16-year-old boy was hit over the head with a metal bar near Oxford Ice Rink in Oxpens Road at about 10.45pm following an altercation with three men.

The attackers, who were about 18 and wearing dark clothing with hooded tops, told the student to hand over his wallet but he ran off and flagged down a bus.

It was the latest in a string of attacks and robberies on foreigners this summer.

Call police on 08458 505505 or Crimestoppers on 0800 555111.