(Updates after the union decided to reject the offer)
SANTIAGO, April 20 (Reuters) - A union of flight attendants for LATAM Airlines subsidiary LAN Express rejected a new contract offer from the Chile-based carrier on Friday, continuing a 10-day-old strike that has affected more than 270,000 passengers.
The 1,000-member Cabin Crew Union of LAN Express said 91 percent of its members agreed to reject the new offer.
"This is a message to the company that we must to sit down and talk. We must reach an agreement," union President Silka Seitz told a news conference.
The offer had included more rest time during work rotations, one of the union's key demands. But it also would have also extended benefits to non-unionized workers, a sticking point that had led the union to vote down another contract offer earlier this week.
In a statement, LATAM said it regretted the union's decision and had no option but to look at extending its reduction in flights.
"We are truly sorry for the hassles and inconveniences caused for our passengers, who have been the hardest hit," Claudia Sender, LATAM's vice president for passengers said. "We've made every possible effort to reach a deal and will continue to do so."
Earlier this week, LATAM said it had canceled a total of 1,575 flights through April 25 while negotiations with the union continued.
The strike has primarily affected flights within Chile, the company said, though it has also affected regional connections throughout South America.
Long-distance flights outside the region have not been affected, LATAM said.
LATAM was created in 2012 through a merger of Chile's LAN and Brazil's TAM. The company, headquartered in Santiago, has operating units in Argentina, Brazil, Chile, Colombia, Ecuador, Paraguay and Peru.
(Reporting by Felipe Iturrieta and Antonio de la Jara, Writing by Dave Sherwood and Mitra Taj; editing by Jonathan Oatis and Cynthia Osterman)