The war between the United States, Israel and Iran has spiralled throughout the Middle East and caused a worsening energy bottleneck in the Strait of Hormuz, the route for about a fifth of global crude shipments.

The US president said on Monday his administration was speaking with an unidentified "top person" among Iran's leadership, as he extended by five days a deadline to hit the country's power plants.

But Tehran's parliamentary speaker Mohammad Bagher Ghalibaf insisted "no negotiations" were taking place, accusing Trump of seeking "to manipulate the financial and oil markets".

Beijing remains a key partner of Iran, but has said it "does not go along" with Tehran's strikes on Gulf states hosting US bases and has urged a ceasefire.

According to China's foreign ministry, Wang Yi told Abbas Araghchi he hoped "all parties can seize every opportunity and window for peace and start the peace talks process as quickly as possible".

The Iranian foreign minister said vessels could "safely pass through" the strait, except those belonging to "countries currently engaging in conflict", the statement added.

He also told Wang that "the Iranian side is committed to achieving a comprehensive end to the conflict, not just a temporary ceasefire", and thanked China for its humanitarian assistance.

The call was held "at the request" of the Iranian side, according to the ministry.

Trump had been due to visit Beijing this month, but postponed the trip to deal with the war's fallout and has urged China and others to help reopen the Strait of Hormuz.