Budget airline Ryanair carried over 100m passengers for the first time in 2015, while its monthly traffic in December surged as the carrier cut fares to encourage passengers to travel after the terrorist attacks in Paris in November.

The Irish group said the number of passengers it carried in the final month of 2015 rose 25% year-on-year to 7.5m, while its load factor – a key gauge in the aviation industry as it measures the number of seats filled per flight – rose three percentage points to 91%.

On a yearly basis, the Dublin-based airline broke the 100m passengers barrier for the first time, as it took its passenger tally for the year to 101.4m, a 17% year-on-year increase, after expanding its winter timetable and reaping the benefits of late-summer tourists flocking to the Mediterranean from northern European countries.

"We are pleased that over 101 million international customers chose to fly with Ryanair in 2015, as we became the first airline to reach this international traffic landmark," said Ryanair's chief marketing officer Kenny Jacobs.

Meanwhile, Ryanair's direct competitor, easyJet, carried 7% more passengers than in 2014, as it reported 69.8m customers flew with the airline during the last 12 months.

The Luton-based carrier also reported a solid increase in passenger numbers in December, although, at 4.6% for 4.8m passengers, the rate of growth was below that of its Irish rival.

EasyJet reported a slight decline in load factor, which fell approximately two percentage points to 86.6%, as a result of a reduction in bookings in the wake of the Paris attacks.

"This strong performance is despite the predicted reduction in bookings in the weeks following the terrorist attacks in Paris," the airline said in a statement.

"EasyJet is France's second largest airline and around 23% of the airline's capacity ‎during December was on French touching routes, and as a consequence the load factor fell to 86.6%. Load factors are now recovering to normal levels and management do not anticipate any change to full year market expectations."