The ancient city of Herat is Afghanistan's best-kept secret.
For years, it has enjoyed 24-hour electricity and a booming economy, reports CBS News chief foreign affairs correspondent Lara Logan.
But it's not thanks to U.S. efforts - it's all because of Iran.
The city lies right on Afghanistan's border with Iran, fueling strong economic ties. But lately Iran's been making a different kind-of investment - one increasingly worrying to the United States: it's backing the Taliban.
A soldier from 7th Group Special Forces finds rocket propelled grenades in a hard-core Taliban village that he knows from experience, are made in Iran.
"Like right here, it says 82 mm "h-e" lot 02 slash 87," the solider said. "The Iranians pretty much copy all of our ordinance, pretty much verbatim. They'll even put English writing on there. But these lot numbers you'll never see a U.S. lot number like that."
The find confirms what U.S. commanders and troops in Afghanistan are seeing more often - a rise in the level of cooperation between Iran and the Taliban.
"I think Iran feels threatened," said David Kilcullen, a counterinsurgency expert. "And I think it feels that its interests are best served by being able to hurt the United States in Afghanistan."
The west of Afghanistan, bordering Iran, is fast becoming a graveyard for U.S. forces. U.S. deaths there have spiked from four a year since the war began, to 13 in the last five months alone.
U.S. military officials have told CBS News that Iran is sending money and weapons onto the Afghan battlefield. But U.S. commanders are not allowed to comment publicly and it's unclear to them what the U.S. strategy is for dealing with Iran's increasingly deadly involvement.
The deadliest form of roadside bomb on the Iraqi battlefield - explosively formed penetrators (EFPs) - is now being found in Afghanistan.
Lethal armor piercing bombs that can slice through U.S. humvees are also an Iranian specialty.
More worrying still: U.S. intelligence believes Iran is supplying surface to air missiles to the Taliban - the very same weapon the U.S. supplied to the Afghan resistance to bring down the Russians.
"We are losing this war every day," said Bruce Reidel, with Brookings.
Reidel led the Obama Administration's strategy review of Afghanistan and Pakistan earlier this year. But he's also worried about Iran.
"It's clear that U.S.-Iranian relations now are going to go into an increasingly difficult period," Reidel said. "If I was sitting in Teheran, I'd be looking for the place where you could hurt the Americans the most and that's Obama's war right next door in Afghanistan."
Iran knows the U.S. is already stretched to the limit in southern and eastern Afghanistan, so opening a new front in the west can only make it even more difficult for the U.S. to succeed.
"It is more violent already but it could get a lot more violent yet," Reidel said. "In a sense Iran has fired a few warning shots across our bow."
That growing Iranian threat means there is even more at stake for the U.S. in Afghanistan than ever before.
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