BRUSSELS/SAN FRANCISCO (Reuters) - Facebook Inc toughened its rules on political advertising in Europe on Friday under pressure from EU regulators to do more to guard against foreign meddling in the bloc’s upcoming legislative election. Chastened since Russia used the social media platform to influence polls that swept U.S. President Donald Trump to power, Facebook says it has ploughed resources and staff into safeguarding the ballot across 27 EU nations on May 26.

FILE PHOTO: A 3D printed Facebook logo is placed on broken glass above a printed EU flag in this illustration taken January 28, 2019. REUTERS/Dado Ruvic/Illustration/File Photo

“I don’t want anyone to be in any doubt that this is a top priority for the company,” Richard Allan, Facebook’s vice president for global policy solutions, told reporters over a video-link to Brussels.

All such ads will be labeled as “paid for”, offering info on who bought it, for how much and how many people have seen it - broken down by age, location and gender.

Only advertisers located and authorized in a given country will be able to run political ads or issue ads there, mirroring policies elsewhere where the tools have been rolled out.

Ads will also be archived for seven years in a publicly searchable archive.

Facebook will block ads that fail to comply from mid-April.

Despite requests by the umbrella political groups that make up the European Parliament and by the EU executive to allow for one-stop-shop pan-European advertising, Facebook said the risks were too high and the timeline too short to do so.

“The convenience ... we understand why they want that, but we could not find any way to carve that out without opening up opportunities nobody would want to see,” Allan said.

Doing so when polls in each of the 27 EU member states are governed by local election rules, he said, would allow little recourse for regulators in case of a breach of law.

The ad transparency rules - already in place in the United States, Britain, Brazil, India, Ukraine and Israel - will be rolled out globally by late June, the company said.

Issue categories differ by country. In Europe, they will be: political values, immigration, security and foreign policy, civil and social rights, environmental politics and the economy.

In the same update, Facebook said it was adding new features and information to its ad archive, the Ad Library, and expanding access to its database so researchers can conduct more in-depth analysis of the data.

Other efforts by the company to safeguard a ballot in which 350 million adults can vote include working with independent fact-checkers to combat disinformation and a cyber security team working to foil bad actors and fake accounts.

As the polls approach, EU heads of state again sounded the alarm at a summit last week, urging private operators such as online platforms and social networks to “ensure higher standards of responsibility and transparency.”

“Over the past year there has been huge progress in awareness of the problem,” said a senior diplomat from an EU member state in the former Soviet bloc, whose government was among those pushing Brussels to pay more attention to the threat. “Now it is becoming a central part of EU thinking ... to address the fragilities that our democratic systems may have.”