Diplomatic source says Israel in 'constant contact' with Russia after downed jet

Israel has been in "constant contact" with Russian officials, both diplomatically and militarily, a diplomatic source said on Tuesday.
Overnight on Monday, an Israeli strike in Syria resulted in the deaths of 15 Russians after a Syrian anti-aircraft missile struck the jet in response. On Tuesday, Israel "expressed regret" for the incident.
The source said Israel is providing Russia materials for its investigation into the incident.