VIENNA—European powers will take the first step towards re-imposing international sanctions on Iran in the coming weeks if Tehran further violates the 2015 nuclear deal, diplomats said.

The warning, an escalation of European pressure on Iran, puts the two sides on a collision course. A conflict is likely in early January, when Iran is set to announce fresh steps to breach the deal. Iranian officials say their moves respond to Europe’s failure to protect them from the impact of withering sanctions the U.S. imposed after President Trump withdrew from the nuclear accord last year.

While Britain, France and Germany say they want to save the nuclear deal—which limited Iran’s nuclear program in exchange for economic incentives—they have warned Iran that they will trigger a dispute-settlement mechanism written into the nuclear deal if Iran continues escalating its nuclear program. Triggering the mechanism, which diplomats say may yet happen later this month, could lead to the United Nations Security Council re-imposing international sanctions on Iran’s economy, banks and some top officials within two months.

The European warning comes as senior Iranian, European, Russian and Chinese officials met in Vienna on Friday to discuss threats to the 2015 deal. In a joint statement, the group called for “full and effective implementation by all sides” and to “pursue all efforts to preserve the agreement.”

Speaking after the meeting, Abbas Aragchi, Iran’s deputy foreign minister and top nuclear negotiator, said that all parties agreed that “without Iran benefitting from” the nuclear deal, “this international agreement cannot be continued,” according to Iran’s state-owned IRNA news agency.