Aircraft lessor BOC Aviation Ltd on Thursday said its 18 planes leased to Russian airlines had a book value of $935 million and could be affected by sanctions and insurance policy cancellations after Russia's invasion of Ukraine.

"The international aviation insurance markets are progressively cancelling certain elements of insurance policies in relation to aircraft located in Russia or leased to Russian airlines," the lessor said in its financial results. "This is a complex and rapidly developing situation that we are monitoring closely."

BOC Aviation, which has 4.8% of its assets by book value leased to Russian airlines, is among the first leasing firms to pubicly confirm upheaval in the aviation insurance market.

The resulting flood of claims and potential writedowns could trigger a lengthy contest between lessors and insurers over liability, according to experts.

(Reporting by Jamie Freed in Sydney Editing by David Goodman )