NATO's secretary general has offered his condolences to Pakistan's prime minister over the death of 24 Pakistani soldiers, describing the apparent NATO airstrike as a 'tragic unintended incident.' 'I have written to the Prime Minister of Pakistan to make it clear that the deaths of Pakistani personnel are as unacceptable and deplorable as the deaths of Afghan and international personnel,' Anders Fogh Rasmussen said in a statement issued Sunday by NATO headquarters. 'This was a tragic unintended incident. I fully support the ISAF investigation which is currently underway. We will determine what happened, and draw the right lessons,' Rasmussen said. He said NATO remained 'strongly committed to work with Pakistan' in order to avoid a repeat of such tragedies and to ensure 'Afghanistan does not once again become a safe haven for terrorists.'