BASRA, Iraq, Nov 1 (Reuters) Business is booming on the Iran-Iraq border.
Despite a war in one country and Western sanctions against the other's nuclear programme, trucks full of everything from fresh produce to furniture and clothes to consumer electronics trundle to the 1,400 km frontier every day.
But British officials say along with trade in legitimate goods, which has grown in the past year, there is also a steady flow of ''lethal aid'' from Iran to Iraq, including rockets and explosives used to make road-side bombs.
Iran denies arming Iraqi Shia Muslim militias, which have carried out scores of deadly attacks against British and American troops in Iraq.
But British officials are sure Iranian weaponry is coming through. As evidence they mention rocket shrapnel that bears Iranian markings, but at the same time say they have no concrete proof that Iran is supplying Iraq.
''It's fair to say that no one has caught anyone red-handed bringing in lethal aid across the border,'' said Major Anthony Lamb, who oversees training of Iraqi border enforcement units.
''Hundreds of searches are carried out every day, but as yet, there hasn't been a direct seizure of lethal aid.'' Lamb says on some days, when British forces visit the major border crossing points in southern Iraq, they can see some Iranian trucks turning back, but there's no certainty they're doing so because they're carrying illicit weapons.
''They could be carrying ladies' underwear and be embarrassed about that,'' he said.
SHEEP SMUGGLING What's likely, those who monitor the border say, is either that corruption in the form of bribes is allowing weaponry to come through, or smugglers are managing to move small amounts at a time across the vast, porous border.
As well as being nearly 1,500 km long, the border is mountainous in the north and marshy in large parts of the south, making it ideal for clandestine movement. Nomadic tribes have also long made their home along large sections of the frontier.
''Trade between tribes on either side has existed for centuries. The border means nothing to them,'' said Lamb.
''For some, economic smuggling has long been a way of life. They might smuggle sheep, or other things.'' Since the invasion in 2003, the United States has built hundreds of ''forts'' along Iraq's borders, including more than 60 along a 500-km stretch along the edge with Iran in the south.
Each fort is manned by 12 to 40 guards who carry out frequent patrols, although the frontier, heavily mined since the Iran-Iraq war in the 1980s, is not fenced. The Iranians have guards all along their side too, visible in the near distance.
As well as the forts, there are two battalions of Iraqi border commandos trained to hunt down smugglers and staunch the flow of illegal goods into the country.
At the two official border crossings in the south, where as many as 300 trucks a day arrive from Iran, customs and border police have managed to crack down on the movement of drugs, illegal cars, banned perishable foods and other illicit goods.
But so far, nothing approximating a rocket has been found.
''They're either not smuggling it through there, or we're looking in the wrong place,'' said a British intelligence officer wryly. ''But one way or another, it's coming in.'' REUTERS RJ ND2353