Ukrainian forces are believed to be behind the multiple explosions on Tuesday at the Saki base in Russian-occupied Crimea, which damaged or destroyed some eight aircraft, as well as ammunition stockpiles.

No one has officially claimed responsibility and it remained unclear Friday exactly what caused the explosions at the base, a major staging point for Russia's war against Ukraine.

Russia has called the incident an accident, but analysts say satellite photos and ground videos suggest an attack.

The United States has supplied large amounts of weaponry and ammunition to Ukraine, but nothing that could allow them to strike from Ukraine-controlled territory that far into Russian-occupied areas.

"We haven't provided anything that allows or that would enable them to strike into Crimea," a senior US defense official told reporters.

The official specifically said it could not have been a US precision-guided, medium range tactical missile, known as ATACMS, which Kyiv has requested and which can be launched by US-supplied HIMARS systems already in Ukraine.

"It was not ATACMS, because we have not given them ATACMS," the defense official said.

The official added that the Pentagon had no information to indicate whether or not there was a missile attack on the base, or whether it was an act of sabotage.

Nevertheless, the official said, it had a "pretty significant impact to Russian air (operations) and air personnel."

British Defence Intelligence said Friday that the multiple huge explosions recorded on video by people in the area "were almost certainly from the detonation of up to four uncovered munition storage areas."

It said at least five Su-24 fighter-bombers and three Su-30 multi-role jets were destroyed or seriously damaged by the blasts, but that the airfield remains usable.

"Saki was primarily used as a base for the aircraft of the Russian Navy's Black Sea Fleet," British Defence Intelligence said.

"The fleet's naval aviation capability is now significantly degraded," it added.