Cancellation plans come because of a planned strike by a union representing cabin crew in Germany.
Lufthansa said on Wednesday it was scrapping 1,300 flights as German cabin crew pressed ahead with a two-day strike, plunging passengers into travel chaos amid an escalating row over pay and conditions.
"As a result of the strike, around 180,000 passengers will be affected by 1,300 flight cancellations," the airline said in a statement after losing a last-minute court battle to halt the walkout.
The 48-hour stoppage called by the UFO flight attendants' union is due to start at 2300 GMT on Wednesday and last until 2300 GMT on Friday.
The union said the stoppage would affect all Lufthansa departures in Germany during that time.
Germany's largest airline said it "regrets the inconvenience for the passengers".
The carrier was putting together an alternative flight schedule where possible, it said, adding that affected passengers could rebook their journeys for free or swap their domestic flights for train tickets.
The announcement of 700 flight cancellations on Thursday and roughly 600 on Friday comes after a Frankfurt labour court denied Lufthansa's request for an injunction to block the strike.
The court ruled that the strike was legal.
Hoping to still avert the upheaval, Lufthansa CEO Carsten Spohr has invited UFO and two rival unions for last-ditch talks on Wednesday evening.
The UFO union has said the strike was necessary because negotiations with Lufthansa bosses were deadlocked.
The union already staged a day-long warning strike last month at four Lufthansa subsidiary airlines, causing several dozen flight cancellations at Eurowings, Germanwings, SunExpress and Lufthansa CityLine.
But the Lufthansa brand was spared after management offered a surprise two-percent pay rise to avoid flight disruptions at its flagship unit.
Since then, however, UFO said no progress had been made in talks.
In addition to higher pay for cabin crew across the Lufthansa group, UFO is demanding more benefits and easier routes into long-term contracts for temporary workers.
Lufthansa bosses, meanwhile, believe that UFO does not have the right to represent workers after an internal leadership tussle and have challenged the union's legal status in court.
Months of infighting have cost the union members and support among cabin crew, some of whom have now turned to other representative organisations.