KABUL, Afghanistan – Winter in Afghanistan is always a hardscrabble time, but this year the season’s bite has been sharpened by a growing shortage of fuel. And because the dwindling supply is due to an Iranian blockade, the dispute is further tangling complicated dealings with a powerful neighbor.

For the last five weeks, a traffic jam of fuel tankers, now swelled to about 2,500 vehicles, has been backed up at the Iranian-Afghan frontier, with only a fraction of the usual number allowed to pass. The resulting shortages were initially felt most keenly in the agricultural south and west. But in recent weeks, the effects have spread to the crowded, car-choked capital, Kabul, with higher pump prices, longer lines and ever-shortening tempers.

As often happens, some of the resentment is aimed at a highly visible target: the 150,000-member North Atlantic Treaty Organization force. Iranian officials have blamed the chokehold on “technical reasons” but also have suggested that at least some fuel ends up in the hands of the Western military.

NATO’s International Security Assistance Force, which is composed largely of U.S. troops, has stated repeatedly that its supply routes do not run through Iran. But the denials are to little avail; the belief that Americans are indirectly responsible for the fuel shortage has taken hold strongly among many Afghans.

Analysts say a likelier culprit is regional muscle-flexing, with Afghanistan cast in its familiar role as the pawn of great powers. When Iran feels squeezed by the United States, it can in turn put the squeeze on Afghanistan, where few tasks are easier than stoking resentment against the unpopular administration of President Hamid Karzai.

“All this is because we have no real government,” said a student who gave his name only as Hamayoon, fuming after a pricey fill-up for his Toyota.

A potential break in the crisis came Tuesday, when Karzai’s office announced that Tehran was prepared to ease the restrictions in coming days provided that Afghanistan spells out for Iran its fuel requirements. But Afghanistan has previously balked at, in effect, petitioning Iran for permission to import what it needs.

Afghanistan is entirely dependent on the outside world for fuel, and between one-third and half of it passes through Iran. Afghan officials have talked of trying to develop direct supply links with neighbors such as Turkmenistan and Uzbekistan. But in the meantime, Iran has a heavy hand on the spigot.

In this instance, Iran’s motivation is murky. Some observers have pointed to continuing U.S. pressure over its nuclear program.

“Above all, for Iran, it’s a way of showing power,” said Haroon Mir, an independent political analyst in Kabul.

The fuel shortage has been blamed for an overall creeping up of food prices, including for staples such as cooking oil, and hikes in the cost of crucial items such as firewood, which is used to heat most Afghan homes and often needs to be transported long distances. In this impoverished country, where children pick through trash for saleable items and burqa-clad widows beg for small change in the street, the winter months mean cold and hunger for many.

Some of the anger against Iran has boiled over into street protests, including rock-throwing demonstrations at the Iranian Consulate in Herat, the nearest large Afghan city to the western frontier. Protesters also have gathered in recent weeks outside the Iranian Embassy in Kabul, galvanized not only by the developing fuel crisis but also by reports that Afghan laborers in Iran have been mistreated.

Iran then fanned the flames by calling on Afghan authorities to crack down on such demonstrations, stirring indignant sentiment over this perceived affront to Afghan sovereignty. Even so, Afghan officials are treading carefully, mindful of the importance of Iranian patronage.

Only this week, after the near-embargo had been in place since mid-December, did Commerce Minister Anwar-ul-Haq Ahady term Iranian actions “unfortunate.”