By Stephen Sackur BBC Washington correspondent

US Defence Secretary Donald Rumsfeld is a supremely confident and uncluttered analyst of what is going on "on the ground".

When I interviewed him this week, I found that his view of the conflict and why America must pursue it and win was very clear-cut.

There is no doubt that Mr Rumsfeld believes, like everyone else in the Bush administration, that this is an existential struggle with an enemy that wants to kill Americans and to destroy America.

Mr Rumsfeld fully expects the US to be attacked again, and as he considers how to respond, he sees a world where the US must go on the offensive to root out evil and to protect itself.

Bluntly, he sees a dangerous world where Americans must either kill or be killed.

No euphemisms

Unlike many officials in governments around the world, Mr Rumsfeld does not use euphemisms. He tells it like it is.

He does not shy away from words like killing.

It is indicative of a man who knows what this war is about, knows how he is going to prosecute it and knows it is going to take a long time to achieve the results he wants to achieve.

Mr Rumsfeld believes the US must go on the offensive

Asked at one point how concerned he was about further attacks, he said straight out, "I expect them."

He did not equivocate. He did not say additional attacks were a concern.

He simply said that he expected further attacks, which was why the US believed that this would be protracted battle and that the war would not end in Afghanistan.

Mr Rumsfeld talked about efforts to aid the Philippines in fighting Islamic insurgents and of his concern about possible terrorist activity in Somalia.

Moral self-assuredness

His self-assurance helps explain his response to questions about US treatment of prisoners taken to the US military base at Guantanamo Bay Cuba.

Mr Rumsfeld made it plain that he did not care whether the treatment of the prisoners raised international concern.

Rumsfeld: Prisoners will face better conditions in the US than in Afghanistan

He chopped the air with his hand as he said that the US, having been hit hard by "the enemy", had an absolute right to bring them here, to interrogate them and to deal with them in a way that America saw fit.

And he reiterated that these were dangerous people.

For him, focusing on the way that the prisoners are being treated conveniently leaves out the fact that these people are killers. They are the hardest of the hardcore - and they are extremely dangerous.

He does not apologise for America or for the aggressive, simple language he uses.

To him, the goals are clear. He is confident that the US will win the war on terrorism, but only at the end of a long and dangerous campaign.