Americans

Four US citizens were kidnapped by armed men on 3 March while driving into the city of Matamoros in the north-eastern state of Tamaulipas, Mexico, across the border from Texas.

BBC reports they had travelled there for cosmetic surgery, relatives told US media.

One man, named only as José "N", 24, from Tamaulipas, has been arrested.

White House National Security Council spokesman John Kirby said: "We offer our deepest condolences to the friends and families of those who were killed in these attacks."

His comments, as he arrived in Poland for a Nato summit, came after two more black men died in such incidents.

Philando Castile was shot dead during a traffic stop in Minnesota on Wednesday, while Alton Sterling was shot dead by police in Louisiana a day before.

Mr Obama said the US must say "we're better than this", and that its importance went beyond race.

"This is not just a black issue. It's not just a Hispanic issue. This is an American issue that we should all care about," he said.

"All fair-minded people should be concerned."