(Reuters) - EU foreign ministers will approve tighter sanctions on Iran over its disputed nuclear activity on Monday, with steps to block oil and gas investment and curtail Tehran's refining and natural gas capability.

A declaration prepared before the meeting showed that as well as adopting harsher sanctions, the foreign ministers would call on Iran to resume talks over its nuclear activities, which Western powers say are aimed at producing atomic weapons."This is increased pressure on Iran to enter into negotiations about their whole nuclear programme,"British Foreign Secretary William Hague told reporters as he arrived for the meeting in Brussels."I hope Iran takes from this message that European nations are open to negotiations about the nuclear programme, but if they don't respond, we will intensify the pressure." While EU ministers were expected to approve the extra sanctions later on Monday, the measures will not legally come into force until they are published in the European Union's official journal on Tuesday or Wednesday, diplomats said."

The annex is extremely detailed and sets out precisely which Iranian entities -- banks, insurance companies, shipping and cargo lines -- are blocked," one diplomat said. "Once it's published, there is a legal obligation to comply."As well as further limiting the activities of Iranian trading banks and insurers, including limits on money transfers to Iran, the sanctions are designed to prohibit new investment in and technical assistance to Iran's "refining, liquefaction and liquefied natural gas" sectors, EU documents show.