Three children aged 5, 8 and 11 and a teacher were killed after a 16-year-old suspect opened fire in the city of Bend, local police say.

The alleged plot only failed because the 19-year-old suspect's gun jammed outside the place of worship, say police.

Two people were severely injured and evacuated by helicopter but no one's life appeared to be in danger, officials said.

A number of states have confirmed they were targeted by the mailings, including Oklahoma, Ohio and Louisiana.