Conservative leader David Cameron says he believes a stable Iraq is possible as "the alternatives are frankly unpalatable".
He said the situation in Iraq, where the government says almost 2,000 civilians died in sectarian violence in December alone, was "truly dreadful".
Mr Cameron, who visited Iraq last year, said a political settlement between Sunni, Shia and Kurds was needed.
This would "show that this Iraqi government can and will work."
"There can be a coming together, but there has to be a real exercise of political will amongst those at the centre to say 'we're going to make this country work, we want a whole Iraq and not a broken one' and they're going to have to really focus on security " he told BBC Radio 4's Today programme.
With the Iraqi Prime Minister Nouri Maliki stating that he dislikes being the country's leader and would prefer to leave the job before his first term ends, Mr Cameron said there was "a huge amount of work" to make the government "stronger".
Mr Cameron, who met Mr Maliki during his November visit, said: "The key to the future of Iraq is for there to be a settlement at the centre between Sunni, Shia and Kurd that they are going to make this country work, that they are going to form a compact together to disarm the militia, to make sure their writ runs through the country.
"Of course we have a role in helping them to do that, but in the end it must be an Iraqi government that gets its act together."
The Conservatives supported going to war in Iraq - a view still held by Mr Cameron, but he now questioned decisions made since the 2003 invasion.
"I still believe it was right to get rid of Saddam Hussein, but I think decisions made subsequent to the war have been extremely poor."
With US President George W Bush expected to announce plans to increase US troops in Iraq, Mr Cameron said a similar plan by the British government would not be a good move, unless it was part of a "broader strategy" to bring stability.
The UK has about 7,000 troops in the south of Iraq, mostly around Basra.
He added his concerns about the execution of former Iraqi leader Saddam Hussein, saying the images of the moments before his hanging where he was taunted were "frankly pretty grisly".
"The way it was handled with people shouting and gesticulating was quite wrong.
"I am glad the Iraqi authorities are going to have an investigation and review into this."