WASHINGTON, March 25 (Reuters) - Iraq has emerged as a more stable country than Afghanistan, thanks to lower violence, the presence of a large U.S.-led international force and high oil prices, according to a report published on Tuesday.

The report by the British-based Jane's Information Group ranked Afghanistan as the world's third most-unstable country after the Gaza Strip and West Bank, and Somalia.

By contrast, Iraq was at No. 22 where it appeared among several African countries including Niger, Nigeria, Burundi and Equatorial Guinea.

The report, titled "Jane's Country Risk Ratings," was the first of its kind for the publisher and contained no comparison figures. But a June 2007 ranking of failed states by Foreign Policy magazine called Iraq the world's second-most unstable country with Afghanistan at No. 8.

Meanwhile, the United States failed to rank among the top tier of the world's most stable countries in the ratings, which measured 235 countries, territories and entities according to two-dozen stability factors.

Vatican City was ranked most stable, followed by Sweden, Luxembourg and Monaco. But Jane's judged the United States to be only the 22nd most stable country -- just below Australia and Portugal -- due to international drug trafficking and the proliferation of small arms within U.S. society.

"Iraq is more stable than Afghanistan," said Christian Le Miere, managing editor of Jane's Country Risk, which complied the ratings.

He said Iraq has benefiting from several stabilizing factors including the world's highest number of international troops per capita, an economy buoyed by high oil prices and a sharp decline in violence.

"With the combination of international troops, the government can extend its will to any area under its administration," he said.

"Compare that to Afghanistan, where the government has less control over its territory, the economy is made up by some estimates about 50 percent from opium and has very little to draw on for resources."

Afghan violence has grown steadily over the last two years to the highest level since U.S.-led forces ousted Taliban rule after the Sept. 11 attacks on New York and Washington in 2001, despite the presence of 43,000 NATO-led troops.

But in Iraq, violence is down more than 60 percent since last summer when the Bush administration completed its buildup of forces known as "the surge." There are currently about 160,000 U.S. troops in Iraq.

U.S. officials attribute the drop in violence to several factors including the troop build-up, a cease-fire by anti-U.S. radical Shi'ite cleric Moqtada al Sadr and the emergence of U.S.-allied Sunni tribesmen.

The Bush administration is now in the process of withdrawing five combat brigades from Iraq by July and could draw down more troops later in 2008 after an expected pause.