By Enda Curran 

HONG KONG--German insurance giant Allianz SE said a unit which acted as lead reinsurer on the two lost Malaysia Airlines flights this year is also the underwriter for AirAsia, whose jetliner went missing Sunday with 162 people on board.

Indonesian officials on Monday said that they suspect AirAsia Flight 8501 is "at the bottom of the sea" after losing contact with air traffic control less than an hour after takeoff on Sunday morning en route to Singapore from the Indonesian city of Surabaya.

"We can confirm that Allianz Global Corporate & Specialty U.K. is the lead reinsurer for AirAsia for aviation hull and liability insurance," a company spokeswoman said in emailed remarks. "We stand by to support our client as fully and quickly as possible, working in conjunction with the insurance broker and our co-reinsurers."

Aviation reinsurance is usually split between providers covering the loss of passengers and the plane, and a separate policy that covers the plane against a malicious act.

Private insurance contracts taken out by the passengers are separate.

Write to Enda Curran at enda.curran@wsj.com

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