A grenade has been thrown at police in Londonderry.
No-one was injured in the attack in the Creggan area of the city. Children were nearby at the time.
Police Chief Superintendent Stephen Martin said: "It is only by sheer good fortune that we do not have a fatality on our hands.
"I am appalled at the callous disregard and recklessness of those who threw the grenade at police, especially as a number of children were close to officers at the time of the attack.
"My officers should be allowed to carry out their duties without the added pressure of misguided individuals intent on causing them harm."
Police said the device in the Southway part of Creggan, a staunchly nationalist estate not far from the city centre, was viable but did not explode. Dissident republicans opposed to the peace process are being blamed.
Police were in the area dealing with a suspect device discovered earlier.
SDLP Assembly member Mark H Durkan said: "This dangerous attack could have led to serious injury or loss of life for the police trying to serve our community.
"It could also have a detrimental impact on police response times to any criminal incidents, particularly in the Creggan area of our city.
"This type of activity is futile, senseless and is rejected by the majority of people in Derry."