Foreign Secretary William Hague said on Sunday he was confident the European Union would impose far-reaching sanctions on Iran's oil industry and possibly other sectors at an EU meeting next week.
He also said he hoped the 27-member European bloc could agree on further sanctions against Syria within the next 10 days over its military crackdown on protesters but gave no details.
EU states have agreed in principle to ban imports of Iranian oil over Tehran's nuclear programme. They are working on details of how the ban will be implemented before a January 23 foreign ministers' meeting.
Iran has threatened to stop the flow of oil through the Strait of Hormuz if foreign sanctions are imposed on its crude exports, a move that could trigger military conflict with economies dependent on Gulf oil.
We must not be put off further sanctions by bluster or statements from Iran. This is an increasingly dangerous situation that Iran is developing a military nuclear programme, Hague told Sky News. Iran denies seeking nuclear weapons.
I am confident we will adopt very significant additional measures against Iran at the European Foreign Affairs Council a week tomorrow, on the 23rd, covering the oil sector and possibly other sectors as well, he said.
Britain is one of six world powers that has been dealing with Iran over its nuclear programme. The West suspects Iran seeks to develop nuclear weapon capability under the guise of its declared civilian atomic energy programme.
Hague said that if Iran continued on its dangerous course it would lead to nuclear proliferation across the Middle East that would be extremely dangerous for the people of Iran, for the region and for the peace of the world.
Our sanctions are part of trying to get Iran to change course and to enter negotiations and we should not be deterred from implementing those. We will continue to intensify our own sanctions and those of the European Union.
Britain was not calling for military action against Iran over its nuclear programme but had not ruled out supporting any option, Hague said.
He denied any British involvement in the killing of an Iranian nuclear scientist last week and declined to speculate on who might be behind it.
Iranian state television said on Saturday Tehran had evidence Washington was behind the assassination, the fifth attack of its kind in two years. The United States has denied involvement.
Britain shut Iran's embassy in London and expelled all its staff after the British embassy in Tehran was attacked last November by a crowd angry at British sanctions. Britain also closed its Tehran embassy and evacuated its staff.
(Reporting by Adrian Croft; Editing by Mark Heinrich)