BEIJING - A Chinese official says the explosion and sinking of an Iranian oil tanker in the East China Sea was without precedent, creating enormous difficulties for rescue and recovery efforts.

Transport ministry official Zhi Guanglu on Friday said the sinking of the Sanchi after a Jan. 6 collision with a grain freighter was a first for a tanker carrying natural gas condensate.

The disaster cost the lives of the tanker's crew of 30 Iranians and 2 Bangladeshis, only three of whose bodies were recovered. The cause is under investigation.

Cleanup efforts continue and China's State Oceanic Administration said it had detected an oil slick in the area that appeared to contain heavy bunker oil from the Sanchi's fuel tanks that could pose a serious threat to the marine environment.