Tony Blair was pushed into supporting military action 'too early' by America determined to take on Iraq, Britain's UN ambassador at the time of the invasion has claimed.

Sir Jeremy Greenstock said the then prime minister had been sincere in his efforts to secure a second UN resolution that would have explicitly authorised the war.

But US officials were uninterested in the idea and pressed ahead with plans for the invasion regardless, he said.

In memos from Tony Blair to George W Bush exposed by the Chilcot Inquiry yesterday, there is evidence of the UK trying to push the US down the United Nations route.

Sir Jeremy Greenstock, left at the UN in 2002 alongside his US counterpart John Negroponte passing resolution 1441, has said after the Chilcot Inquiry that US officials were not committed to tackling Iraq through the United Nations despite Tony Blair's efforts

Sir Jeremy told the BBC: 'I felt that at the time, the British felt it at the time, I think the prime minister felt it at the time, that the Americans pushed us into going into military action too early.

'The Americans weren't genuine about it - but the prime minister was genuine about it - because he thought there was a chance that Saddam could be made to back down before we had to use military force.

'And George Bush for a while agreed with him. But other people behind George Bush didn't agree with him and thought it was a waste of time.'

General Tim Cross, Britain's most senior official involved in planning the invasion, said the Americans had also undermined aftermath planning - insisting it was a US decision to dismantle the Iraqi Army and ruling Ba'ath Party.

He told the broadcaster: 'That particular decision was approved by the president of the United States, the secretary of defence, by the joint chiefs of staff of the United States.

'It was previously discussed by my national security adviser with authorities in London 10 days before it was issued - he received no objections.'

The US state department has declined to comment on the findings of the report or the claims levelled at the US government.

A spokesman told the BBC: 'We are not going to examine it, we are not going to try to make an analysis of it or make judgement of the findings one way or another.

'Our focus is on the challenges we have in Iraq and Syria right now.'

Mr Blair, seen leaving home this morning, was subject to harsh criticism in yesterday's Chilcot Inquiry into the Iraq War

Sir John Chilcot ruled in his damning inquiry the 2003 invasion was not the 'last resort' when it had been launched and there were further diplomatic channels which had not been exhausted.

Mr Blair has insisted he successfully directed the US to pursue the UN approach but that it became clear it would not work.

In a crucial memo from Mr Blair to the president dated July 28, 2002, Mr Blair said: 'I will be with you, whatever. But this is the moment to assess bluntly the difficulties.

'The planning on this and the strategy are the toughest yet. This is not Kosovo. This is not Afghanistan. It is not even the Gulf War.'

He urged him the military part of the plan was 'hazardous' but said getting rid of Saddam was 'the right thing to do', adding that 'containment… is always risky'.

Jack Straw last night disagreed with the Sir John conclusion that diplomatic options had not been exhausted at the time of invasion.

'With the benefit of hindsight, different decisions would have been made on Iraq, and the inquiry sets out the clear lessons which need to be learnt,' he said.

'The consequences which flow from the decision to take military action against Iraq will live with me for the rest of my life.

'But the decisions made by me and others can only properly be judged in the context of the time. I take full responsibility for all those that I made.'