Iran had taken and concluded what he characterised as a proportional response.

句子有几个重点：

1. taken and concluded 并列，共有一个宾语：what he characterised as a proportional response，而意义上的核心宾语是 response。 意为“采取并总结了他所描述的成比例的回应”。

2. 这里，characterize 作“描述,  描绘” 解，常用于“characterize + 宾语 + as + n./adj. ” 结构。 意为“把......描述为......”，本句，what 是宾语，as ...作宾补。

3. 这种结构，在英语中比较常见。例如：

We are going to visit what we know as a famous place.

We are going to visit what is known as a famous place.

我们要去参观众一个所周知的著名的地方。

I lived in what you call “Ancient Greece.” 

I lived in what is called “Ancient Greece.” 

我生活在你们所说的“古希腊”。

【翻译】伊朗已经采取并总结了他所描述的成比例的回应。