At the Tehran office of the Japanese daily Asahi Shimbun, staff keep one eye on CNN and one on the Iranian news channel. But for the Japanese government, balancing the US and Iran is becoming harder as Washington raises pressure on Tehran over its nuclear programme.

Tokyo’s warm relationship with Tehran goes back to 1953, when the Japanese tanker Nissho-maru defied a British blockade imposed after Iran’s prime minister, Mohammad Mossadegh, nationalised the oil industry. Today, Japan is Iran’s biggest export market for crude.