Russia has highly likely lost at least four combat jets in Ukraine within the last 10 days, taking its attrition to about 55 since the beginning of its invasion, the British military said on Monday.

There is a realistic possibility that the uptick in losses was partially a result of the Russian Air Force accepting greater risk in a move to provide close air support to Russian ground forces under pressure from Ukrainian advances, the Defence Ministry said in its daily intelligence on Twitter.

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Russian pilots’ situational awareness is often poor, it said.

“There is a realistic possibility that some aircraft have strayed over enemy territory and into denser air defence zones as the front lines have moved rapidly.”