The biggest airline in the US has cancelled another 900 flights after safety concerns forced it to ground 300 of its aircraft.

It is the third day of cancellations by American Airlines. More than 2,400 flights have been affected, causing delays for 100,000 passengers.

The action follows an inspectors' warning of problems with wiring repairs on the MD-80 aircraft two weeks ago.

Other major US carriers have also been forced to ground planes for inspection.

Southwest, Delta and United are among those affected, and the US Federal Aviation Administration (FAA) said it could not rule out further groundings as it widens aircraft safety investigations in the next two months.

The FAA has been tightening up its inspections since it was discovered last year that fuselage cracks on Southwest planes had gone undetected because of missed inspections.

Safety inspections

The US Senate is due to hold its latest set of hearings on airline maintenance and inspection later on Thursday.

The MD-80 aircraft grounded by American Airlines on Wednesday make up nearly half of its passenger-carrying fleet.

Chief executive Gerard Arpey has apologised to customers for the inconvenience.

"American will do whatever it takes to assist those affected by these flight changes, and our employees are working hard to ensure that we remain their choice for air travel," he said.

The FAA said it had checked several American MD-80s and decided that improvement work carried out did not meet its standards.