BRUSSELS, July 2 (Reuters) - A group of European Union and U.S. Democrat lawmakers has asked the International Energy Agency to develop international standards for measuring the oil and gas sector's emissions of methane, to help countries adopt tougher measures targeting the potent greenhouse gas, a letter showed on Tuesday.

The EU will impose methane emissions limits on Europe's oil and gas imports from 2030, but has yet to confirm how the exact limit will be calculated. Currently, there is no international agreement on how firms should count and verify claims about the emissions associated with their gas.

In a letter to IEA executive director Fatih Birol, seen by Reuters, seven EU lawmakers - including representatives from the two biggest lawmaker groups in the European Parliament - and ten U.S. Democrats asked the energy watchdog to help develop international standards for measuring methane emissions from the oil and gas sector.

"We would kindly suggest issuing a report with your recommendations for these international standards and processes, if possible by June 30, 2025," said the letter, dated July 1.

The aim, the letter said, would be to help countries develop policies to clamp down on methane emissions. It asked the IEA to help countries adopt policies that apply methane standards to fossil fuel imports, and analyze the possible impact of this on oil and gas prices.

Methane is the main component of the gas burned in power plants and to heat homes. It is also the second-biggest cause of climate change after carbon dioxide, and contributes to global warming when it escapes into the atmosphere from leaky oil and gas pipelines and infrastructure.

The U.S. last year set out its own rules requiring domestic oil firms to limit their methane emissions.

The letter's signatories included representatives from the EU Parliament's two biggest lawmaker groups - the European People's Party and the Socialists and Democrats - as well as the Parliament's negotiators on the EU methane law, Green lawmaker Jutta Paulus and liberal Pascal Canfin.

The 10 signatories from the U.S. house of representatives were all Democrats. (Reporting by Kate Abnett; Editing by Susan Fenton)