At least 78 people have been killed and more than 115 injured in western Ukraine, when a military aircraft crashed into a crowd of spectators at an air show.

Thousands of people watched in horror as the Russian-made Sukhoi Su-27 jet plummeted from the sky, exploding into flames amongst the crowded stands, in what has become the world's worst air show disaster.

About 115 people are thought to have been injured in the disaster

The Defence Ministry has begun an inquiry and said it suspected that engine failure was to blame.

President Leonid Kuchma, who visited the scene at the Skniliv airfield near Lviv, said he wanted to ban air shows of this kind.

He has also dismissed both the air force chief and the commander of the air force division which took part in the show.

The Ukrainian Government has set up a $2m fund to help families of the victims, and a national day of mourning will be observed on Monday.

Ball of fire

About 1,500 people were watching the free air show, part of celebrations to mark the 60th anniversary of a local air force unit.

There weren't any survivors among those who fell down late - they were cut down like grass

Bohdan Hupalo Spectator

Witnesses said the jet was performing complex aerobatic manoeuvres before it clipped some trees and another plane, cart-wheeled across the ground and crashed in a huge ball of fire.

The two-pilot crew managed to eject from the aircraft, and were led away badly shaken.

The plane hit the crowded spectator stands, and scores of bodies were strewn across the tarmac.

The Emergencies Ministry said the number of deaths could rise still further because many of the injured were in critical condition.

There were scenes of panic as parents searched for their missing children.

The jet was performing complicated manoeuvres

"I could only grab children and hold on. We were thrown away, and hands and legs were flying all around us," said Zinovy, one of the spectators.

Bohdan Hupalo, 18, said he dived to the ground and saw the jet race over him, missing him by only a few metres.

"There weren't any survivors among those who fell down late - they were cut down like grass," he said.

'Real nightmare'

President Kuchma broke off his holiday in the Crimea to fly to the scene of the disaster, describing it as "a real nightmare".

He pledged more than $1.9m from the federal budget in an initial fund for the victims.

"I will see that no family goes without government aid," he said.

Mr Kuchma even announced his intention to ban military air shows completely, saying the air force "need to do their business, not take part in these shows".

He declined to speculate on a possible cause of the crash, but he did say that the equipment might have been exhausted beyond its limits.

"We don't know anything absolutely except that the pilots were the most experienced, of the highest class," the president said.

According to the BBC's Nikolai Gorshkov, the cash-strapped Ukrainian air force cannot afford to buy spare parts for its ageing jets, and President Kuchma said restructuring of the armed services was a priority.

The Soviet-designed Sukhoi-27 is a big long-range air fighter, comparable to the US F-15.

Analysts say that in air shows it has demonstrated an exceptional controllability at high angles of attack.

Aviation specialist Paul Beaver says a disaster such as this could not have happened in western Europe, where crowd lines and display organisations would ensure that, even if something did go wrong, an aircraft would never fly directly into the crowd.