Foreign Secretary William Hague said Iran should "be more realistic about what is necessary" to reach a nuclear deal with major powers.
Hague made the comments shortly after a meeting with US Secretary of State John Kerry in Vienna.
They were joined in the Austrian city by their French and German counterparts for talks about Iran's nuclear programme.
Six months ago, a deadline to reach an agreement was set for July 20.
More top news
Mild in the south but colder in the north tonight and turning frosty and icy - before rain moves in.
ITV News' Tom Brady speaks to billionaire philanthropist Bill Gates about clean energy sources and a new $7bn green tech research fund.
A man accused of killing three people and wounding nine others in a shooting at an abortion clinic in Colorado has appeared in court.