BRUSSELS — NATO and European Union governments are considering new ways to respond to suspected Russian sabotage, cyberattacks and other threats against critical infrastructure, but allies have yet to agree on a forceful, immediate strategy. The discussions follow a series of incidents across Europe, including a Russian drone strike that hit a train near the Polish-Ukrainian border over the weekend and Bulgarian investigations into two explosions at weapons-storage sites. European officials have also raised concerns about an alleged attempt to target Leipzig-Halle Airport in Germany last month. Three NATO diplomats and a person familiar with the discussions said allies are informally considering whether a pattern of attacks below the threshold of conventional war could eventually trigger Article 5, NATO’s mutual-defense provision. No consensus has emerged, and the alliance has not formally adopted a plan. The debate reflects a difficult balance for European governments. A response that is too weak could invite further attacks, officials and lawmakers warn. A response viewed by Moscow as a direct escalation could increase the risk of a broader conflict with Russia. “We have all the response options,” NATO Secretary-General Mark Rutte said Monday, adding that some measures would be public and others would not. He warned Russian President Vladimir Putin that continued attacks would bring a response while saying NATO would continue supporting Ukraine. A senior NATO diplomat described the current approach as “keep calm and carry on,” while acknowledging that pressure was rising after the incidents near Poland. A senior European defense official said intelligence services had so far prevented the most serious attacks, but cautioned that Europe had also been fortunate that no major incident had caused widespread casualties. “We are too shy — definitely,” said German lawmaker Marie Agnes Strack-Zimmermann, chair of the European Parliament’s defense committee. “Vladimir Putin never stops, he’s always coming closer … we have to show we’re willing to fight back.” Potential measures under discussion include faster, coordinated decisions to attribute attacks to the Kremlin, stronger protection for hospitals and other civilian infrastructure, and pre-arranged packages of sanctions or other responses. NATO members are also expected to account for spending on civil preparedness and infrastructure protection under a commitment to devote 1.5% of gross domestic product to such activities by 2035. The alliance has not fully defined which expenditures will qualify. Gerlinde Niehus, a former NATO official and independent security expert, called for response plans agreed in advance by governments and intelligence agencies. She said Russia could exploit the slow decision-making that often separates NATO and the EU, warning that a serious attack without a clear alliance response could damage NATO’s credibility. Rutte rejected the suggestion that NATO would appear weak if it did not immediately announce new measures, while declining to say whether the alliance was developing additional options. EU governments face their own internal disagreements. European Commission President Ursula von der Leyen is expected to emphasize defense, security and hybrid threats in a policy address this week, with a broader EU security strategy due in the coming weeks. EU foreign policy chief Kaja Kallas is preparing sanctions against about 1,600 entities, although those measures were proposed before the latest weekend incidents. The European Parliament is also expected to approve a nonbinding resolution describing Russia as the most serious hybrid threat facing the EU and its member states. Another report would call for expanded powers and resources for EU agencies working against hostile state activity. At the same time, EU governments failed Monday to extend sanctions covering roughly 3,000 Russian individuals and companies, underscoring the political obstacles to a unified response. Gabrielius Landsbergis, Lithuania’s former foreign minister, urged European governments to take more aggressive steps, including targeting Russia’s shadow fleet in the Baltic Sea and expanding Ukraine’s drone production. He also advocated offensive cyber measures. The competing pressures leave European residents, businesses and public institutions facing a widening security challenge without a clearly defined common response. NATO officials are weighing how to deter further attacks while avoiding a confrontation that could widen the war beyond Ukraine.