Delta Air Lines, America's third-largest carrier, will lay off about 4,000 employees because not enough workers volunteered for the redundancy packages on offer.

The carrier said last October it would cut up to 8,000 of its 76,000 workers because of lower demand for air travel.

But so far only about 3,900 employees have accepted voluntary severance packages and early retirement offers.

The rest will now be laid off.

Most of the job cuts at the struggling airliner will be completed by 1 May.

The Atlanta-based air carrier expects to take $175 million in charges to cover for the job cuts.