Dushanbe: US Secretary of State Hillary Clinton implicitly warned Iran on Saturday not to interfere in neighbouring Iraq after President Barack Obama announced all US troops will leave Iraq by year end.

"As we open this new chapter in a relationship with a sovereign Iraq, to the Iraqis we say: ‘America is with you as you take your next steps in your journey to secure your democracy," Clinton said on a visit to Tajikistan.

"And to countries in the region, especially Iraq's neighbours, we want to emphasise that America will stand with our allies and friends, including Iraq, in defence of our common security and interests," she said.

"We will have a robust continuing presence throughout the region, which is proof of our ongoing commitment to Iraq and to the future of that region, which holds such promise and should be free from outside interference to continue on a pathway to democracy," Clinton added.

Obama said on Friday all American troops will leave Iraq by the end of the year, ending a long war which cleaved deep political divides and estranged the US from its allies.

In Iraq, Prime Minister Nouri Al Maliki said the US military's withdrawal is a "historic occasion" that will transform ties between the two nations.