(adds detail) JERUSALEM, Sept 23 (Reuters) - An explosion was heard in central Jerusalem on Sunday but police said it was not an attack but rather a controlled blast at a building site. "There was a controlled explosion carried out by a contractor doing construction near Jerusalem's central bus station," said police spokesman Micky Rosenfeld. Israel has been on alert for possible attacks in recent weeks. Police said they seized an explosives belt on Saturday that was intended to be used in a Tel Aviv suicide bomb attack.
