An Egyptian man was arrested and referred to prosecutors on Wednesday for throwing four homemade nail bombs into the grounds of the German embassy in Cairo and vandalising the entrance of the building with a hammer. No one was hurt in the incident, nor was any serious damage caused, embassy and security sources said.

According to Adel El-Tonsi, chief prosecutor for West Cairo, investigators found the culprit, 54-year-old Ahmed Khaled, to be "psychologically unstable."

Khaled confessed to carrying out the attack, telling investigators that he had acted out of anger after reading a newspaper report on Friday about a recent protest by right-wing activists in Germany who had reportedly paraded caricatures of the Prophet Mohamed in front of a German mosque.

General Hany Gerges, head of Cairo's Qasr El-Nil Police Station, received a report on Wednesday morning from a German embassy employee stating that someone had attacked her. The assailant, Gerges said, had issued threats against the German government before being arrested by police.

Ahmed confessed to having come to the embassy early Wednesday morning, where he engaged in a heated exchange with an embassy employee before throwing three packs of gunpowder – which did not ignite – inside embassy grounds.

"It was just one person who attacked the embassy and damaged the glass of the entrance with a hammer," said a German embassy spokeswoman. "There was no major damage and no one was hurt."

Khaled had also brandished a toy pistol, she added, and had used a hammer to crack the embassy's glass entrance. He had also brought copies of the newspaper article with him.

Police who arrived at the scene found Ahmed with two full packs of gunpowder, nails, a knife and a toy gun.