WASHINGTON - During the Cold War, the United States and the Soviet Union avoided fighting each other directly, with both great powers fearing direct battles could escalate into a nuclear war. Instead, they supported opposing sides in conflicts in Afghanistan, Angola, Korea, Vietnam and other hotspots around the world.
Analysts now say that the U.S. and Iran could be at the start of the same sort of "proxy war" in Iraq, perhaps the first such conflict in the new era of warfare since the end of the Cold War.
The latest verbal shot was fired Sunday when U.S. military officials in Baghdad accused "the highest level" of Iran's government of supplying Iraqi militants with armor-piercing roadside bombs called "explosively formed penetrators," or EFPs, that have been responsible for the deaths of 170 members of the U.S.-led coalition.
When President Bush recently accused Iran of providing weapons and training to militias attacking U.S. troops in Iraq, he said U.S. forces would kill or capture Iranian operatives in Iraq but would not attack Iran directly.
"We've known for a while that Iran was providing lethal aid to the insurgents, we're just finally pushing back," a senior administration official said last week in an interview. "Iran has to understand that it is not getting a free pass anymore."
In turn, Tehran's ambassador to the United Nations, Javad Zarif, accused the U.S. in a column Thursday in The New York Times of "trying to make Iran its scapegoat and fabricating evidence of Iranian activities in Iraq."
With the ratcheting up of tensions, analysts say the potential for a misstep looms large.
"The worst case is that there's an accidental war," said Robert Malley, Middle East program director for the International Crisis Group, an independent research organization. "Neither side may think it's in their best interest, but they have to hit back to show they're not doing nothing."
Along with the recent verbal sniping have come a number of armed confrontations.
Last month, U.S. soldiers raided an Iranian office in the northern Iraqi city of Irbil, detaining five Iranian officials. The U.S. also moved a second aircraft carrier battle group to the Persian Gulf, and positioned more Patriot anti-missile batteries in the region.
On Jan. 20, militants kidnapped and killed four American soldiers in an ambush at a U.S. military base in the southern Iraqi city of Karbala. U.S. military officials in Baghdad are investigating whether Iranian agents were involved, surmising that it could have been payback for the Irbil raid.
The administration says it has known for about six months about Iranian "networks" providing aid and weaponry to Shiite militants, but only recently decided to go after them in a more systematic way.
Iran has responded with more rhetoric, though Iran-watchers say the response has been milder than in previous times, and that President Mahmoud Ahmadinejad appears to be in a weak position domestically.
Iranian supreme leader Ayatollah Ali Khamenei said in a Thursday speech broadcast on state television, "The enemy knows well that any invasion would be followed by a comprehensive reaction to the invaders and their interests all over the world."
The growing face-off has put Iraqi officials in a difficult situation. Historically, Iran has maintained strong relationships with top Shiite Arabs and Kurdish leaders. During part of the long regime of Iraqi President Saddam Hussein, Iran served as a haven for such political leaders as current Iraqi Prime Minister Nouri al-Maliki and Abdul Aziz Hakim, the leader of the Supreme Council for Islamic Revolution in Iraq. Iran also armed Kurds led by Jalal Talabani, who is now Iraq's president, in the midst of internecine fighting between Kurds in the mid-1990s.
Some analysts of Iran argue that it has no interest in inflaming a sectarian war in Iraq, because of the potential for a huge refugee crisis in Iran. "Iran doesn't want a failed Iraq but a weak Iraq," one Iraqi official said.
In the Irbil raid, U.S. forces seized computers and files from a purported intelligence office. But some Iraqi officials, including the foreign minister, have accused U.S. forces of taking a heavy-handed approach against the Iranians inside Iraq.
"Iran has the choice now of going underground and being less active, or accelerating its efforts to hurt the Americans where they can," said Qubad Talabany, who represents the Kurdistan Regional Government in the U.S. "We're worried that America will do something without assessing the situation. The last thing we want is two powerful countries fighting a war on our turf, but maybe it's inevitable."