U.S. and Iraqi forces man a border crossing between Iraq and Iran but Iranian weapons still find their way into Iraq. A dusty border speck on the map where tanks once fought a bitter war in a brutal landscape, trucks now stretch to the horizon, a sign of growing contact between former blood enemies. Iraqi patrol guards in an observation tower high above an Iran/Iraq border crossing, in the eastern Iraqi province of Wasit, monitor people and goods crossing from Iran, identifying suspect trucks which are then searched by hand when they cross. Tensions still simmer and the border crossing at Zurbatia has become an outpost of U.S. and Iraqi efforts to stem the flow of Iranian weapons and agents into Iraq's south and east. Hundreds of trucks, piled high with bright yellow and green melons, bags of onions, building supplies and furniture, queue for miles every day on the Iranian side of the border, waiting to bring in imports on which Iraq's shattered economy relies. Buses wait to unload tour groups of religious pilgrims headed for Iraq's Shi'ite holy sites. Iraqis head the other way to Iran for medical treatment they can't get at home and to escape Iraq's remorseless heat. Washington and the U.S. military accuse Shi'ite Iran of funding, training and arming Shi'ite militias in Iraq with roadside bombs, including armour-piercing "explosively formed penetrators". Tehran denies the charge. The U.S. military this year launched a "surge" of 30,000 extra troops in a last-ditch bid to stop the slide to civil war, aimed both at al Qaeda fighters and Shi'ite militias. Part of that effort has focused on stemming the flow of weapons. Wasit province's part of the Iraq-Iran border stretches for 143 km, (90 miles) so it is unlikely weapons smugglers would try to get through a heavily guarded checkpoint complete with two "back scatter" x-ray machines scanning every vehicle for arms. "When we first got here about a year ago there was literally a gate and almost an open field where people and commerce passed," said Colonel Mark Mueller, commander of a U.S. military unit working with Iraqi border guards in Wasit province. "But there was a lot of challenges for security," he said. Mueller said about 2,000 Iraqi guards patrol Wasit's stretch of the border. The checkpoint sits on a slim finger of land jutting from Iran into Iraq, surrounded by desert and mountains to the east, a quarry where trucks send up choking clouds of powdery dust. In the past 11 months huge open-sided sheds have been built where incoming and outgoing crowds now wait in separate queues while their passports are checked and their baggage searched. A maximum of 1,500 Iranians a day are permitted to cross into Iraq at Zurbatia, with no limit on Iraqis entering Iran. Porters in blue overalls earn about 30 U.S. dollars a week in tips pushing ramshackle carts piled high with baggage, the old and infirm, black-shrouded women and children. New computers allow Iraqi immigration officials to process the crowds, with high-tech biometric scans used to seek out anyone on U.S. or Iraqi wanted lists. Once processed, they head to two very low-tech metal gates. A green gate on the Iranian side was once the only barrier, sometimes allowing up to 500 people through at a time, overwhelming Iraqi border officers. U.S. soldiers threw together a few concrete blocks a couple of metres away to form three walls, swung a gate between two of them and painted it white so that Iraqi officials now also have a say in how often people come through and in what numbers. Up to 450 trucks a day also queue at the Zurbatia border checkpoint, Wasit's only official port of entry. Fuel trucks are the only Iranian vehicles that are allowed to cross. Everything else must be "transloaded" -- Iranian trucks are driven up to a holding area where their loads are shifted to Iraqi vehicles. Passengers on buses must alight and walk across. Some Washington and U.S. embassy officials in Iraq have noted recent improvements in Iran's involvement in Iraq but the U.S. military says Iranian weapons and components are still being found in Iraq. Iranian-made weapons were among a large cache of arms and ammunition found during operations in a Shi'ite militia stronghold south of Baghdad, the Iraqi army said on Monday (November 19). Major-General Jamil Kamel al-Shimari, a senior officer in the 8th Iraqi Army Division, said the cache was the biggest store of weapons found since the launch of operation 'Lion Pounce' on Saturday (November 17). The stockpile, which included roadside bombs, rocket-propelled grenades, mortar bombs and explosives, was uncovered in Diwaniya, 180 km (110 miles) south of Baghdad. Four suspected militants were arrested at the scene, among 74 who have been detained since the operation began. An unidentified Iraqi soldier showed weapons laid out on the ground, "This is an anti-tank mine. It is Iranian made," he said, pointing at writing on the top. "We have found one of the biggest weapons caches in the city centre of al-Diwaniya. The cache contained roadside bombs that have been manufactured outside Iraq. There were about eight or nine as well as 82 mm and 60 mm mortars," said another unidentified Iraqi soldier. U.S. and Polish helicopters and soldiers supported Iraqi security forces in the Diwaniya operation, said Polish military spokesman Lieutenant-Colonel Wlodzimierz Glogowski. The operation, which Glogowski said includes two Iraqi army battalions and one police brigade, is trying to squeeze militants out of the area. Qadisiya province, of which Diwaniya is the capital, has been spared much of the sectarian bloodshed that has rocked other parts of Iraq. But it has been hit hard by factional fighting between rival Shi'ite militias, including the feared Mehdi Army loyal to influential anti-American cleric Moqtada al-Sadr. Shi'ite militants have attacked military bases, including those used by about 900 Polish troops in Qadisiya.