Brown insists that US is Britain's strongest ally

Gordon Brown will today insist that America remains Britain's most important ally as he attempts to draw Europe and the United States into a new drive to make the United Nations "fit for purpose" in the 21st century.

He will welcome closer links between the White House and France and Germany, and press for redoubled efforts to reform the UN to allow it to tackle problems of climate change and global terrorism.

The Prime Minister will use his annual Guildhall speech on foreign affairs – his first since taking over in No 10 – to reassure the White House that Britain remains a close friend of the United States. But he will also use the speech to signal this Government's independence from the White House by emphasising Britain's position as part of a "network of relationships around the world".

Yesterday Mr Brown attempted to heal the international rifts that have opened up over the invasion of Iraq to insist that there was a "great opportunity" to reform international bodies established after the Second World War. He praised relations between Britain and the US, which have been marred in recent months by friction over British troop withdrawals from Iraq and the appointment of Lord Malloch-Brown as a Foreign Office minister despite his criticism of the United States while a senior UN diplomat.

Asked about possible future attacks on Iran, Mr Brown said "nothing should be ruled out", but insisted diplomacy was starting to work. Mr Brown also signalled he would not be a slavish supporter of the US.

Mr Brown told Sky News: "It's important to recognise that over the next few years as European countries like France and Germany move closer to America, there's a great opportunity for all of us to work together to reshape the international institutions, to make them fit-for-purpose for the decade that we are in, rather than the decade in which the international institutions were created in the 1940s."

He added the EU and US could "achieve a great deal" by working more closely together to face up to the challenges of global warming, failed states, security and global pandemics.

Britain has already made clear that it favours expansion of the permanent membership of UN Security Council from the current five nations – the US, Russia, China, the UK, and France – to 10 nations by including the so-called G4 nations – Japan, Germany, Brazil and India – as well as a representative from the African continent.

The Government has also backed organisational reforms of the New York- based body to make it more responsive to humanitarian and political crises.

The talk of reform comes after Mr Brown has moved to distance himself from Mr Blair's foreign policy since he took over as Prime Minister in June.

In September, the Foreign Secretary, David Miliband, acknowledged that mistakes were made over Iraq and promised to learn lessons from the "scars" of the war.

Yesterday Mr Brown moved to emphasise a future policy of multilateral action over such issues as Iran in an attempt to address fears that British foreign policy under his predecessor was too close to that of the Bush White House.

In doing so, he emphasised the breadth of Britain's relationships around the world. "We are part of the European Union, we're part of Nato, we're part of the Commonwealth, and the Commonwealth heads of government meeting will be held in Uganda very soon.

"The strength of our relationship with America is incredibly important to the future of the world," he said.

He argued that France and Germany were "moving closer" to the United States and had a major opportunity to reform the way international problems are tackled, insisting that it "is to the advantage of everyone ... that France and Germany and the European Union are also moving more closely with America."

Mr Brown continued: "I think what people recognise is that what has changed perhaps over the last period of time, is that as France and Germany and the European Union move closer in understanding to America ... [it] enable[s] us to build better international institutions that can deal with today's problems."