KARACHI, Pakistan — It was happening again, but worse than ever: Hundreds of thousands of ethnic Rohingya Muslims were fleeing Myanmar while under attack by the security forces, and the deaths kept mounting.

Everybody in the vast Arkanabad slum of Karachi has family members who were affected by the government raids that started last month.

Outside Myanmar, and perhaps now Bangladesh, Pakistan is home to the highest concentration of Rohingya in the world, from a previous exodus of Rohingya in the 1970s and ’80s. A vast majority live in neighborhoods that are distressingly impoverished even by Karachi’s standards.

Now they are angry that Pakistan is not doing more to stop the killing in Myanmar, let alone improve the condition of the estimated 500,000 Rohingya who live in this country.