Tony Blair today made his strongest attack yet on the Iranian government, declaring that President Ahmadinejad's government was a "major strategic threat" to the Middle East.

Despite calls from the James Baker-led Iraq Study Group for direct talks with Tehran and Damascus, Mr Blair said there was "little point" in including Iran and Syria in regional issues "unless they are prepared to be constructive".

Ahead of his own trip to the Middle East before Christmas, Mr Blair repeated that as his premiership drew to a close he still regarded it as the most important issue facing the world.

The prime minister repeatedly reiterated his personal revulsion at the current conference, sponsored by the Tehran government, on the reality of the Holocaust, calling it "disgusting, unbelievable and shocking".

Speaking at his final monthly press conference of 2006, the PM said Mr Ahmadinejad s government was "deliberately causing maximum problems for moderate governments and for ourselves in the region - in Palestine, in Lebanon and in Iraq".

"There is no point in hiding the fact that Iran poses a major strategic threat to the cohesion of the entire region," Mr Blair told reporters.

Mr Blair said that he found the conference organised by Iran which questioned existence of the Holocaust "shocking beyond belief".

"To go and invite the former head of the Ku Klux Klan to a conference in Tehran which disputes the millions of people who died in the Holocaust, what further evidence do you need to have that this regime is extreme?" he asked.

He told a journalist from Israeli radio that the conference was a "disgusting" affront to the millions of families who lost relatives in the Holocaust. It was "such a symbol of sectarianism and hatred towards a people" he added.

More than half the hour-long press conference focused on the Middle East, with Mr Blair quizzed on whether the UK could withdraw from Iraq in advance of the US, or in tandem with it.

He said the situation for UK troops in Basra was different from that for US troops in Baghdad, where there was more sectarian violence, but the UK withdrawal would not be affected by US decisions.

"If and when they [US troops] are able to change the situation in Baghdad, then they too will be in a different set of circumstances, but the pace at which both of those things may happen may be different," Mr Blair said.

Mr Blair said it was still the intention to withdraw British troops once Iraqi authorities were able to take over.

"I certainly do not take the study group as saying that we should get out, come what may.

"What they are saying is that we have to increase our driving up of the capability of the Iraqi forces, because it's obviously better that the Iraqis themselves take responsibility and indeed the Iraqi government is increasingly saying it wants to take responsibility.

"Then the coalition forces will still be in a support role but it won't be the same as it is at the moment."

Asked about apparent UK opposition to the US policy of early de-Ba'athification of Iraq after the invasion, Mr Blair said the problems in Iraq were deliberately being caused by people opposed to the democratic process, and any decision on de-Ba'athification would not have changed that.

On the wider Israeli-Palestinian question, Mr Blair rejected comparisons of the peace process, where the UK government talked to Sinn Féin and the Democratic Unionists even at times when they refused to recognise each other.

"It is very difficult to see how you can negotiate with Hamas in circumstances where they are saying emphatically 'we deny the right of Israel to exist'," he said.

"There has to be a genuine willingness on their part - or at least on the parts of elements of Hamas - to engage in a meaningful way with Israel and I don't notice that at the moment."

Mr Blair said Hamas was being "deliberately unhelpful".

"It is one thing to have a position about Israel which is your formal position ... but if you look at what they have been saying over the past few days it sounds to me, I am afraid, deliberately unhelpful.

"If you add up what has been said over the last few days about Israel - and not always in answer to a question either - then it's quite difficult to see what the way forward is."

The prime minister said he hoped to use his visit to make clear what the Palestinians could expect in return for progress.

"It is important for us to say very clearly 'this is what we will do if you are prepared to accept that any negotiation on two states must be on the basis of mutual respect and mutual recognition.

"One of the things I want to do in the course of the visit is to spell out exactly what we would do in those circumstances, for the Palestinians, including in respect of Hamas."