A senior U.S. official says the U.S. and China differ on how to deal with North Korea regarding its attack on South Korea’s “Cheonan” Navy vessel.

The official, who asked not to be identified, said that with high-level bilateral talks with Washington approaching, China is still unsure about whether North Korea is responsible for the sinking.

The official added that the U.S. and China have also not agreed on the issue of sanctions on Iran.