The Archbishop of Canterbury Dr Rowan Williams has warned that the world faces a "skilful and merciless" enemy in the form of terrorism.
Dr Rowan Williams is known for his outspoken views
In his New Year's message, Dr Williams chose the theme of trust and said the lack of it was badly affecting society.
Some of this lack of trust was due to the threat from terrorism, the archbishop argued.
In his broadcast on BBC Two, Dr Williams said terrorists were "willing to risk everything".
Dr Williams said lack of trust was affecting politics, business and public life "from policemen to vicars".
"We don't know where the enemy is - and it is an enemy who is skilful and merciless and willing to risk everything.
"We may grumble at the constraints and checks - but part of us knows just why we move in this atmosphere of suspicion.
"Once you see the dreadful results of terrorism at close quarters, you can begin to appreciate why everyone comes to be viewed with a degree of mistrust."
The archbishop's warning over terrorism came after he spoke last month about the killing of British consul Roger Short in the Istanbul blasts.
Only days earlier, Dr Williams had been entertained by Mr Short and his wife at their home in Istanbul during a three-day pilgrimage to the city.
But Dr Williams has been very critical of the detention of terror suspects without trial, saying that the holding of people in British jails and in Guantanamo Bay could alienate moderate Muslims.
The broadcast will be repeated on Thursday at 1300 GMT on BBC One.