As the war in Ukraine intensifies, Russian troops are shifting their focus to the country’s east. Parallel to this pivot, Ukrainian troops issued their first allegation of Russian chemical warfare in a Telegram post on Monday. Three fighters reported that Russian forces had released “A poisonous substance of unknown origin” during a drone attack in the besieged Ukrainian port of Mariupol. Fighters suffered minor injuries, according to Al Jazeera; one fighter wasn’t able to breathe and collapsed with “cotton legs.” The B.B.C. writes that this unverified incident was reported the same day that a representative from the Moscow-backed Donetsk People’s Republic urged the use of “chemical forces” in the invasion of Mariupol.

Western nations have warned that the deployment of chemical weapons would mark a severe escalation of the conflict; many have pledged to take “firm action” if such attacks are carried out, including U.S. President Joe Biden. U.K. Defense Minister James Heappey said that he would “rule nothing out” if the allegations of chemical warfare were confirmed. “There are some things that are beyond the pale,” he said. “The use of chemical weapons will get a response, and all options are on the table for what that response could be.” NATO Secretary-General Jens Stoltenberg similarly warned that NATO would “respond proportionately” upon their deployment. The use of chemical weapons would be “a blatant and brutal violation of international law,” he said. Ukrainian President Volodymyr Zelensky echoed these concerns on Monday, saying this would mark a “New stage of terror against Ukraine.” He urged Western nations to arm his troops to defend the country. Authorities from the U.S. and the U.K. are investigating the situation but are yet to find evidence of the claims.

The early assumptions of the investigation suggest that Russian troops used phosphorus ammunition. Ukraine’s Deputy Defense Minister Hanna Maliar notes that under the Chemical Weapons Convention, phosphorus is not classed as a chemical weapon. However, its use as an “incendiary weapon” near civilians is considered illegal, according to The B.B.C. “We know that last night around midnight, a drone dropped some so-far unknown explosive device,” Pavlo Kyrylenko, the governor of the Donetsk region, said. “The people that were in and around the Mariupol metal plant… began to feel unwell,” Reuters noted that the affected fighters were admitted to a nearby hospital and appeared to be healthy a few days after the incident.

The Russian government has yet to comment on their alleged use of chemical weapons. However, on Tuesday, Russian President Vladimir Putin gave his first extended comments on the conflict since last month. Amid allegations of rape, brutality against civilians, and the use of chemical weapons, he defended the war as a “noble” mission, according to Reuters. He stated that “there is no doubt” that the war would accomplish its goal of helping the people in Donbas.

As the conflict escalates, Ukrainian officials urge civilians to evacuate, adding to the 4.6 million refugees that have already fled the country. According to the United Nations High Commissioner for Refugees, most of the refugees are settling across the border in Poland; estimates suggest that Poland is the final destination for more than 2.65 million refugees. Migrants are also flooding into Romania, Hungary, and Moldova. The Washington Post notes that most refugees are women and children, as Ukrainian law prohibits men of fighting age from evacuating. Since the beginning of the war in February, over 44 million Ukrainians – about a quarter of Ukraine’s population – have been displaced from their homes; many will return to their cities burned and bombarded.

If allegations are confirmed, this will mark a significant turning point in the war. It would elicit greater involvement of Western countries, including the U.S., U.K., other members of NATO, and the European Union. Considering “All options are on the table,” it is hard to predict what the response will be. Politico reports that the White House is scrambling to match Biden’s pledge of an “in-kind” response while avoiding further escalation. Unlike European countries, the U.S. has stated that an American military confrontation is not an option to avoid sparking World War III, according to Biden. To start, Western allies could multilaterally steepen sanctions on Russia, including the long avoided sanctioning of oil and gas. Europe’s continued importation of Russian energy has funded troops and fueled the Russian movement into Ukraine. Western allies should also respond to Zelensky’s call to arm Ukrainian forces with advanced weaponry to buttress their defenses.

However, before implementing these measures, the allegations need to be confirmed. On Tuesday, an anonymous European official told Politico that “There’s no independent verification in that area, so it’s likely to be a long time.” A senior U.S. defense official added that there is a “host of difficulties” in substantiating the accusation. “These are difficult things to prove even when you are more proximate, and we are not.” Additionally, U.S. officials have challenged the credibility of the Azov regiment. They are a far-right group that could be politically motivated to inflame the current conflict and provoke a more aggressive confrontation. U.S. officials also pointed out that Ukrainian officials – who have been very quick to point out Russian atrocities – are yet to acknowledge the use of illicit weapons.

As stated by the Pentagon, the allegations are “deeply concerning.” It is of great importance that Western allies take decisive action against the use of chemical and biological weapons. However, they should not act out of haste to avoid unintentionally escalating the war.