Israel and Iran exchanged fire again on Wednesday, the sixth day of strikes between the regional rivals, fuelling fears of a drawn-out conflict that could engulf the Middle East.

"Israel's acts of disregarding international law and international rules have caused the situation in the Middle East to suddenly become tense, and China is also deeply concerned that the situation may get out of control," Wang told his Egyptian counterpart in a phone call Wednesday, China's foreign ministry said.

The same day, in a separate call with Oman's foreign minister, Wang said the two countries "cannot sit idly by and let the region slide into an unknown abyss". He said reaching a ceasefire agreement was a "top priority".

China and other world powers have pushed to find an off-ramp to the hostilities, which began after Israel on Friday launched strikes on Iran.

The United States, however, has called for Iran's "unconditional surrender", with US President Donald Trump on Wednesday saying Washington may still take part in the conflict.

Iran's Supreme Leader Ayatollah Ali Khamenei said Wednesday his nation would never surrender and warned the United States of "irreparable damage" if it intervenes, while Israel said it had destroyed the internal security headquarters in Tehran.