A European Union official, speaking on condition of anonymity, said the Chinese could not attend due to scheduling problems. China, along with Russia, is opposed to a hardening of sanctions against Tehran.
"Negotiations will be taking place over the next few days" to set a new date for a meeting, said a Foreign Office spokesman, on condition of anonymity in line with policy.
Talks between political directors of the five permanent members of the United Nations Security Council and Germany were planned for Monday, and had been expected to take place in Brussels.
Russia's Itar-Tass news agency reported the meeting had been postponed because China had refused to attend.
China's London embassy was not immediately available to comment on Friday.
A report Thursday from the U.N. nuclear watchdog agency found Iran to be generally truthful about key aspects of its nuclear past, but the U.S. and Britain said Tehran's revelations were inadequate and urged new U.N. sanctions.
The U.S. and allies claim Tehran is using a civilian nuclear program as cover to develop weapons. Tehran rejects the charge.
Britain's Foreign Office said Thursday "if Iran wants to restore trust in its program, it must come clean on all outstanding issues without delay."
U.S. officials said that at previous talks in London on Nov. 2 on Iran's nuclear program, Russia and China showed no enthusiasm for imposing a third set of sanctions on Tehran.