The International Energy Agency (IEA) has raised its estimates for oil demand next year but says soaring shale production in America should ensure there are no shortages in supply.

Improving economic conditions in China and the US is likely to result in about 865,000 barrels of extra crude demand during 2013, to reach total consumption to 90.5m barrels a day, according to the IEA’s latest oil report.

That figure is more than 110,000 barrels more than estimated just four weeks ago even though the IEA believes demand will remain sluggish in the first half of the year.

The expected increase in overall demand, plus increasing speculation that America is about to unleash a new round of quantitative easing to further boost the domestic economy, helped to raise Brent crude futures to $109 a barrel.

Meanwhile, a meeting of Organisation of Petroleum Exporting Countries (Opec) ministers in Vienna agreed to hold its official output at 30m barrels a day. But there is unease inside Opec that relatively low-demand growth, accompanied by major increases in American and Iraqi oil production, could lead to a price collapse next year.

Iraq is a member of Opec but made clear it would not help with any production cuts next year even if prices did dip, arguing that other members such as Saudi Arabia, which have previously increased their output, should make cuts first.

After 20 years of war, sanctions and civil strife that left its oil industry in disarray, Iraq is in no mood to consider curtailing output just as it starts to take off.

“Iraq will never cut production,” Iraq’s Opec governor Falah Alamri told Reuters. “Some countries that have increased their production in the last two years – they should do so. This is a sovereign issue, not an Opec issue.”

That was a clear reference to Saudi Arabia, which this summer lifted output to a 30-year high above 10m barrels a day to prevent oil prices soaring after western sanctions on Iran halved its production.

The tensions inside Opec have increased since the overthrow of Saddam Hussein in Iraq and the Arab spring, culminating in a row over who should lead the cartel when the secretary general, Abdalla Salem el-Badri, a Libyan national, steps down.

Neil Atkinson, director of energy research at Datamonitor, said: “Iraq is impervious to arguments. It says that it was subject to sanctions for so long that it has a free pass to rebuild its economy.

“There is rising oil from places like the United States, and Iraqi output is rising quite sharply. There’s a risk that we see a sharp drop in price next year.”

Output from Iraq has increased by 1m barrels a day to 3.4m following the release of service contracts to western oil companies such as BP, Shell and ExxonMobil.

The US Energy Information Administration said on Tuesday that US output would rise by 760,000 barrels a day in 2012, the fastest rate since commercial oil production began more than 150 years ago.