There is grave concern for the safety of witnesses.

证人们的安危受到严重关注。

He expressed grave concern at American attitudes.

他对美国的态度表达了严肃关注。

The police have expressed grave concern about the missing child's safety.

警方对失踪孩子的安全深表关注。

We regard these developments with grave concern.

我们极为关注这些发展。

President Barack Obama calls it a matter of grave concern.

美国总统奥巴马声称这个事一件严肃而且复杂的事情。