A number of homes were evacuated and a pipe bomb was thrown at police during disturbances in Derry last night.
The incident happened close to a controversial nationalist bonfire built in the middle of the main road at the Leckey Road flyover in the city's Bogside.
PSNI district commander Mark McEwan said a viable pipe bomb-type device was thrown at a police patrol.
Sinn Féin MLA Raymond McCartney blamed dissident republicans.
"Several families, including elderly people, had to be evacuated from their homes due to a security alert on Charlotte Street.
"This situation was dictated by a tiny group of young people who are being exploited by more sinister elements who are clearly determined to act against the wishes of the local community."
Foyle DUP MLA Gary Middleton said the person who threw the pipe bomb had put dozens of lives at risk.
"Those who constructed and threw this device are terrorists who clearly have no regard for the lives of anyone in the city."
He added: "We have witnessed too many occasions where such terrorists have held this city to ransom and we must demonstrate that such violence and threat cannot be part of our society."