MANDALI, Iraq - Worried about people sneaking in from Iran, U.S. troops and Iraqi border guards are focusing their attention on the "socket" - a remote section of frontier that juts into Iran and is used by smugglers, shepherds and even jobs hunters for illegal crossings.
The strongest concern, however, is that the rugged area is being used by those helping Iraq's insurgency.
Iraqi and U.S. authorities have long accused Iran of meddling in Iraq, and the border guards and American technology are the first and main line of defense against infiltrators.
The task is a formidable one. The two countries are separated by mountains and rocky hills laced by narrow creek beds that provide numerous hiding places. Hundreds of thousands of munitions left over from the 1980-88 Iran-Iraq war are strewn throughout the area, making patrols even more difficult.
Lt. Col. William M. Hart, who commands the 1st Squadron, 278th Regiment of the 42nd Infantry Division based in Athens, Tenn., said most of the illegal movement across the border has been stopped.
"There's been some contraband, movement of vehicles in and out, smuggling operations," Hart said. But he described the crossings as "small-scale in nature" and said only a small percentage was tied to the insurgency.
Still, there is cause for concern. In February, the 278th Regiment announced it had captured Jaffar Sadiq Fette, a suspected Iranian intelligence agent, in the border city of Mandali. Fette was allegedly involved in the killing of an Iraqi intelligence officer and helped Iraqis go to Iran to train at camps run by the militant group Hezbollah.
Officials have also watched the border more closely as President Bush has publicly confronted Iran over its nuclear program. Bush has said the United States is not preparing to attack Iran, but no option is ruled out if the Iranians do not abandon what Washington views as efforts to build a nuclear bomb.
Iran's government insists its nuclear program is only to generate electricity.
Just under 1,000 Iraqi border guards and about 100 soldiers from the 1st Squadron patrol a 60-mile-long section of the central border with Iran. The regiment's 3rd Squadron watches the adjacent area to the north.
Iraqi guards and soldiers from the U.S.-led coalition, including Polish and British-led forces to the south and Kurdish peshmerga militiamen farther to the north, keep an eye on the rest of the frontier with Iran.
On a hilltop two miles from the border, U.S. soldiers peer out of high-powered scopes, scouring mountainsides for paths used by smugglers and illegal immigrants. While they are keeping watch for anyone who tries to cross, they are particularly focused on foreigners who could be arming or supporting Iraq's insurgency.
The border is a "nightmare to patrol or defend," said Lt. Kevin Mick of Columbia, Tenn.
U.S. soldiers patrol this section of the border one to six times a day, and monitor it with electronic equipment. But even with advanced technology and heavy terrain vehicles, the area is so rugged that soldiers must stay on the main roads - leaving paths hidden in the back country to infiltrators.
"Most of the time, even if we do see (border crossers) we don't catch them because they know the terrain so well," Mick said.
Iraqi border guards caught each of the approximately 200 people picked up crossing the border in February, said Capt. James Hite, a native of Nashville, Tenn. U.S. troops rely on the guards for their knowledge of the terrain and population.
"We don't know if they're Iranian, but (the border guards) can tell the difference," Mick said.
Concerns remain about the border guards' loyalty. During a visit to one Iraqi border outpost by U.S. troops, the Iraqi guards - some in civilian clothing or mismatching uniforms - complained they hadn't been paid in two months and said there was an unequal distribution of weapons between their men and Iraqi army soldiers.
"We're not naive to think some border patrol aren't being paid off," Mick said, adding the guards are paid about half as much as Iraqi soldiers. "But (the border) is a lot better off than what (it) used to be."