In the Islamic approach, life is a divine gift and bestowment to every individual. It has priority and is heading all the human rights. It would be useless and meaningless to talk about any rights before this right has been provided for a society's individuals.
The fundamental of the value of the human life, is the value of human's existence as well as malice and viciousness of killing (assault on man's life).
Therefore killing a person is not considered assault on a man's life, but a murder and assault on the reality of humanity and fading away viciousness and indecency of murder.
إِنَّمَا جَزَاءُ الَّذِينَ يُحَارِبُونَ اللَّهَ وَرَسُولَهُ وَيَسْعَوْنَ فِي الْأَرْضِ فَسَادًا أَنْ يُقَتَّلُوا أَوْ يُصَلَّبُوا أَوْ تُقَطَّعَ أَيْدِيهِمْ وَأَرْجُلُهُمْ مِنْ خِلَافٍ أَوْ يُنْفَوْا مِنَ الْأَرْضِ ۚ ذَٰلِكَ لَهُمْ خِزْيٌ فِي الدُّنْيَا ۖ وَلَهُمْ فِي الْآخِرَةِ عَذَابٌ عَظِيمٌ
Because of that, we decreed upon the Children of Israel that whoever kills a soul unless for a soul or for corruption [done] in the land - it is as if he had slain mankind entirely. And whoever saves one - it is as if he had saved mankind entirely. (Quran, 5:33)
The sanctity for a man's blood is underlined so emphatically in Islam that the value of life and death of an individual equals to the value of life and death of all mankind. The Holy Prophet (S) in his farewell sermon in the last year of his life in Mena, before a crowd of Muslims, while emphasizing on the right of individuals and sanctity for their blood, said: "O people, you have to respect each other's life until the Resurrection Day."1
Moreover, in another occasion, talking about the significance of regarding the human life, he has said, "Before God murdering a believer is worse than destroying the whole world.”2
Again in another occasion he said: "If the residents of the Heavens and the Earth conspire (as accomplices to collaborate) to collectively shed the blood of a believer, God will throw all of them into the fire of hell.…"3
Of course it should not be misunderstood that sanctity of a man's life is exclusively for Muslims, that Islam has not drawn a line for a non-Muslim's life. A non-Muslim's life is honorable and respectable, too, as long as he refrains from involving in opposition or conspiracy against Muslims or an Islamic government.
As the Prophet (S) said, "He, who gives somebody a chance to live (in his blood) and then kills him, he will be subjected to the fire of hell.”4