Baghdad (DPA) -- The US will withdraw its troops from Iraq if the security pact between the two governments is not signed, Iraqi media quoted a senior United States official as saying Wednesday.

'The United States will withdraw its forces from Iraq and refuse to approve an extension of the UN Security Council mandate if the treaty is not signed,' David Satterfield, senior advisor to the US secretary of state and the country's Iraq coordinator, told the semi- official al-Sabah newspaper.

Satterfield met with Iraqi groups opposing the so-called Status of Forces Agreement to try to persuade them to support it, the newspaper reported.

The agreement sets the legal basis for the future presence of US troops in Iraq after a United Nations Security Council mandate expires at the end of the year.

Under the pact, the deadline for the complete withdrawal of US troops - currently standing at more than 140,000 - would be December 31, 2011.

Signed by Iraqi Foreign Minister Hoshyar Zebari and US Ambassador to Iraq Ryan Crocker on Monday, the deal however still needs parliamentary approval before it can be signed by the US and Iraqi presidents.

In Hillah, about 85 kilometres south of Baghdad, more than 5,000 Iraqis including clan chiefs and students demonstrated in support of the pact, witnesses told Deutsche Presse-Agentur dpa.

Chanting slogans urging the Iraqi government to sign the security agreement, the demonstrators carried flags and signs reading: 'Together for the withdrawal of foreign troops from Iraq' and 'With heart, with blood, we save you, Iraq.'

The demonstrators walked to the city council surrounded by hundreds of Iraqi police and soldiers.