Authorities sought to learn more about a decorated ex-US Marine sergeant who killed three police officers in Baton Rouge, Louisiana, some two weeks after police there shot dead a black man.
The Dallas gunman was plotting a major bomb attack, authorities said on Sunday, urging calm as hundreds of people were arrested in weekend protests in US cities over police violence against African-Americans.
Dallas was gripped by a new security scare on Saturday triggered by an anonymous threat in the Texas city, on edge days after a gunman fatally ambushed five police officers during a peaceful protest.
Thousands of protesters took to the streets in US cities on Friday after a black extremist shot dead five cops during a peaceful march against police brutality in Texas.
The World Health Organization (WHO) has voiced concern over a report the Zika virus has been sexually transmitted in the US and called for further investigation into the mosquito-borne virus.
