The strike over plans to expand the company's budget airline Transavia in Europe entered its ninth day at a cost of 20 million euros (USD 25.7 million) daily.
"There is no reason for this strike ... It is jeopardising the image of France and represents a real danger for Air France," Valls told Europe 1 radio.
"This strike must stop. Management has made a number of proposals and it seems to me the conditions are in place for the positions of either side to come together."
Alexandre de Juniac, chief executive of Air France-KLM -- Europe's second largest airline after Lufthansa -- said this was the "last offer" to break the deadlock that has grounded on average 60 per cent of the fleet.
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However the main pilots union rejected the offer as a "smoke-screen that offers no more guarantees than previous offers and does not solve any problem."
The longest strike at Air France since 1998 "has had disastrous consequences for customers, employees and the company's finances," the airline said.
They fear the airline will seek to replace expensive Air France pilots, who can earn up to 250,000 euros a year, with Transavia pilots, who are paid considerably less.
Unions have threatened to extend the strike until Friday unless their demands are met.