The top US military official conveyed his most sincere condolences to Pakistan's army chief Thursday, over a fatal cross-border Nato strike that strained relations between the countries. We take this incident very seriously, Admiral Mike Mullen said in a letter to Pakistan army chief General Ashfaq Kayani, the US embassy said. I wanted to send my most sincere condolences for the regrettable loss of your soldiers killed and wounded on 30 September near your border with Afghanistan.