· Pentagon admits one of 28 loads missing and blames wind · Turkey criticises arms airdrops saying the strategy will never lead to desired results

The Pentagon admitted on Wednesday that one of the airdrops of weapons intended for Kurds in the besieged Syrian town of Kobani almost certainly ended up in the hands of the Islamic State (Isis) fighters.

The Pentagon blamed the wind for possibly blowing the supplies off course and argued that one cache was not enough to make a significant difference to Isis.

Video footage released by Isis shows what appears to be one of its fighters in desert scrubland with a stack of boxes attached to a parachute. The boxes are opened to show an array of weapons, some rusty, some new. A canister is broken out to reveal a hand grenade. Other equipment appeared to be parts for rocket-propelled grenades.

The Pentagon said the pallet of weapons was one of 28 dropped, not six as previously reported.

US defence spokesman Army Lieutenant Colonel Steve Warren said: “One bundle worth of equipment is not enough equipment to give the enemy any type of advantage at all. It’s a relatively small amount of supplies. This is stuff [Isis] already has.”

The Pentagon cleared up some confusion about a cache going astray on Sunday that had subsequently been destroyed in a US strike, once it had been realised it was in danger of falling into Isis hands.

Warren said two caches had gone astray but the air force had managed to destroy one. A steady stream of US-supplied weapons are being lost to Isis forces, mainly from the dysfunctional Iraqi army. Isis is reported to have stolen seven American M1 Abrams tanks from three Iraqi army bases in Anbar province last week.

A spokesman for the Pentagon, Rear Admiral John Kirby, told reporters that analysts at Centcom headquarters in Tampa, Florida, were examining the video. “We’re still taking a look at it and assessing the validity of it,” he said. “So I honestly don’t know if that [box] was one of the ones dropped.” he said.

Turkey’s president, Recep Tayyip Erdoğan, criticised the airdrops strategy, saying it was “wrong” that weapons had fallen into the hands of Isis, as well as the Kurdish fighters they were intended for.

Turkey’s government sees the fighters as part of the Syrian arm of the Kurdistan Workers Party (PKK), a faction that has battled for self-rule in Turkey for over three decades.

“It has become clear that [the airdrops are] wrong,” Erdoğan told reporters in Ankara. “It’s impossible to achieve results with such an operation,” he added.

In an abrupt shift, Turkey agreed on Monday to allow Iraqi Kurdish fighters to cross its territory and reinforce fellow Kurds in the besieged town of Kobani, but did not comment on whether it backed the airdrops.

The US has dropped munitions, supplied by Kurdish authorities in the semi-autonomous region of northern Iraq, to their compatriots in Kobani, which sits close to the Iraqi-Turkish border; Isis fighters have encircled much of the town.

Kirby confirmed the weapons shown in the video were the kind that were dropped. “So it’s not out of the realm of the possibility in that regard,” he said.

“I do want to add, though, that we are very confident that the vast majority of the bundles did end up in the right hands. In fact, we’re only aware of one bundle that did not.”

The airdrops were carried out by three C-130 planes. The video shows a man in camouflage clothes and balaclava looking through the boxes of munitions. He says they were dropped by US forces and had been intended for the Kurds. He described them as the spoils of war.

As well as grenades, the boxes appeared to contain parts for rocket-propelled grenades. Some of the equipment appears to be east European in origin, which might seem odd given the weapons were dropped by Americans, but the munitions were supplied by the Kurdish authorities who had been stocking up.

Kirby said that the situation in Kobani remained tense, with Kurdish forces in control of most of the city. The US-led coalition has mounted more than 130 air strikes round the town in an effort to stop Isis taking complete control.

While the US has carried out air strikes in Kobani, cloud cover last week prevented them hitting much of the rest of Iraq, particularly around the contested Mosul dam. If the dam was to fall to Isis it would provide huge leverage for the group.

Britain has been supplying the Kurdish semi-autonomous region with weapons but so far supplies have been limited. Kurds report receiving about 40 heavy machine guns but say they need heavier equipment, in particular armoured vehicles.