Britain, France and Germany notified the United Nations on Thursday that Iran was in breach of its obligations under the 2015 agreement restricting its nuclear activities and moved to reinstate harsh sanctions suspended in that deal.

The notification does not mean the immediate reimposition of sanctions. It begins a 30-day period of consultation in which Iranian and European diplomats are likely to intensify negotiations to avoid that outcome.

“We will continue to strive to diplomatically resolve the issue,” the foreign ministers of the three European countries said in a statement.

Under the U.N. resolution that governs the deal, no Security Council member can veto the sanctions, even Iran’s allies Russia and China. They are also signatories to the agreement.

The so-called snapback would again impose on Iran extensive penalties that were in place before the 2015 deal. They include an embargo on sales of conventional arms, asset freezes, visa bans and significant restrictions on ballistic missile production.

The 2015 deal expires on Oct. 18. On that day, the sanctions suspended under it would disappear. Triggering the snapback would keep the sanctions in place beyond that date. European officials view the sanctions as leverage to compel Iran to negotiate another agreement over its nuclear activities.