(Reuters) - Air France said on Monday it had proposed a final pay offer to unions in a bid to end costly strikes.

The airline said it was offering an additional pay increase of 1 percent for 2018, taking the overall increase to 2 percent.

For 2019, 2020 and 2021 Air France said it was offering a general wage increase of 5 percent, equivalent to 1.65 percent per year.

The airline said the estimated cost of the strikes, including action planned for April 17 and 18, was 220 million euros (190.1 million pounds).

The pay offer is open up until April 20 at midday local time (1000 GMT), Air France added.

(Reporting by Alan Charlish; Editing by Alexander Smith)