U.S. and European diplomats have jointly condemned a spate of violent attacks in northern Nigeria that have killed 28 people this week.

On Monday, three people were killed and at least three injured in an attack in the northeastern city of Maiduguri. A day earlier, a bombing by suspected Islamic militants in the same city killed 25 people at a beer garden.

In a joint statement Tuesday, EU and U.S. diplomats in Nigeria condemned the attacks, saying there is no place in society for such horrific acts of violence and that there should be no impunity for perpetrators.

The carnage is thought to be the work of Boko Haram, an Islamic fundamentalist group whose name means “Western education is sinful.” However, no one has yet claimed responsibility.

The group claimed responsibility for a separate bombing at Nigeria's police headquarters earlier this month and has been blamed for numerous attacks on police, government officials and religious leaders.

Nigerian officials have offered to negotiate with the shadowy group, but spokesmen have rejected the offer.