Donald Rumsfeld, the US Defence Secretary, warned Iraqi politicians today not to purge the security forces and stack the ranks with their own men.

Lack of confidence or corruption in government would be "unfortunate", Mr Rumsfeld said in Baghdad today on a short and unannounced visit to Iraq.

There are fears that the Shia Muslim and Kurdish parties, which came to power in the January 30 election, could fire Sunni officials in revenge for the decades of oppression they suffered under Saddam Hussein’s regime.

"It’s important that the new government be attentive to the competence of the people in the ministries and that they avoid unnecessary turbulence," Mr Rumsfeld said.

Ibrahim al-Jaafari, the Prime Minister, said after meeting Mr Rumsfeld that he realised the risks to the political process. "I don’t deny there are challenges, but I am sure we are going to form very good ministries," he said.

Mr Rumsfeld also met President Jalal Talabani, the Kurdish former rebel leader. Language caused some problems and both men struggled to make themselves understood to the Iraqi and US journalists. At one point Mr Talabani translated for Mr Rumsfeld after he was asked a question in Arabic.

The President said he had assured Mr Rumsfeld that Iraq’s interim leaders will work together. "We are planning to have the (permanent) government as soon as possible, but you know this is the beginning of democratisation in Iraq," he said.

Mr Rumseld also told the politicians to form a government quickly or risk allowing insurgents to gain momentum. The Government is expected to complete its selection of cabinet ministers before the end of this week.

The next milestone is writing a new constitution by August and ratifying it by a national vote in October.

Mr Rumsfeld also met privately with General George Casey and Lieutenant Gen. John Vines, the top two American commanders in Iraq. Iraqi security forces were now tackling the insurgents more aggressively, Gen. Casey said.

The Defence Secretary also visited several hundred soldiers at Camp Liberty, headquarters of the 3rd Infantry Division. "The role you’re playing is a critically important role in the global war on terrorism," he told them.

It is Mr Rumsfeld’s second visit to Iraq in three months and his ninth since the war began in March 2003. He arrived in Baghdad before sunrise on an Air Force C-17 cargo plane.

The frequency of his visits reflects a desire to push the political and military momentum that he believes has been growing since the January 30 elections.

There has been unrest today in northern Iraq ahead of Mr Rumsfeld’s expected visit to Mosul. Two suicide car bombers have struck near US military patrols, killing five Iraqis and injuring seven.

Meanwhile, Iraq said it captured a former high-ranking member of Saddam Hussein’s Baath Party who is believed to have organised and funded insurgency attacks.

Fadhil Ibrahim Mahmud al-Mashadani, the former leader of the Military Bureau in Baghdad, was apprehended by security forces early today on a farm northeast of Baghdad, the government said.

In a separate operation in southern Baghdad, four leaders of three groups linked to al-Qaeda were captured in a joint US-Iraqi operation that captured 67 suspected insurgents.

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