Alexander Lukashenko has threatened to cut deliveries of gas to Europe via a major pipeline as the Belarusian leader promised to retaliate against any new EU sanctions imposed in response to the crisis at the Poland-Belarus border. Backed by the Kremlin, Lukashenko has struck a defiant note after inciting a migrant crisis at the border, where thousands of people, mainly from Middle Eastern countries, are camped out as temperatures plunge below freezing. Meanwhile thousands marched through the streets of Warsaw to mark Poland’s Independence Day, including far-right groups calling for the government to prevent migrants from entering the country illegally. The city government had banned the march but those orders were overturned by the national government, which is dominated by the conservative Law and Justice party. Polish authorities have taken a hardline stance on the crisis, instituting a state of emergency in the border region that allows police to ignore asylum requests and summarily expel migrants. It also prevents NGOs and journalists from entering the border zone. As punishment for Belarus’ actions, the EU is expected to sanction up to 30 Belarusian individuals and entities, possibly including the national air carrier Belavia. Belarus’s neighbours have said they may be forced to shut their borders. “We heat Europe, and they are still threatening us that they’ll shut the borders,” said Lukashenko in an emergency meeting with his top ministers on Thursday. “And what if we cut off [the transit of] natural gas to them? So I would recommend that the leadership of Poland, Lithuanian and other brainless people to think before they speak.” The threat to cut off deliveries along the Yamal-Europe pipeline from Russia is an attempt to pile additional pressure on Europe, where gas prices spiked last month due to an international energy crisis. Yet it appears unlikely that EU members will back down from a new round of sanctions against Lukashenko, who has already been targeted for a brutal crackdown on his country’s opposition and the grounding of a Ryanair flight in May. Belarusian opposition leader Svetlana Tikhanovskaya said Lukashenko would not follow through on the threat. “It would be more harmful for him, for Belarus, than for the European Union and I can suppose it’s bluffing,” Tikhanovskaya told AFP, urging European countries to hold firm and not communicate directly with the “illegitimate” leader. EU members say that Lukashenko has enabled thousands of people to travel through Minsk and to the EU borders as revenge for the sanctions against him. Belavia, the Belarusian state airline, has strongly denied it is involved in any trafficking of vulnerable people to the border with the EU. Videos posted to social media indicate that the flow of migrants through Minsk has not slowed and that hundreds more people may be arriving at the border every day. Poland reported that there had been 468 illegal attempts to cross the border on Wednesday and that people had attempted to cut through razor-wire or use logs to batter down border fencing in some places. Other countries bordering Belarus have warned that the border crisis could lead to a new military conflict. In a joint statement on Thursday, the defence ministers of Estonia, Lithuania and Latvia called the situation “the most complex security crisis for our region, Nato and the European Union in many years”. Belarus’ use of migrants could lead to “provocations and serious incidents that could also spill over into military domain,” the statement said. In a show of support for Lukashenko, Moscow has dispatched nuclear-capable bombers for the past two days to patrol the skies over western Belarus. The Russian defence ministry has called the patrols, which included imitation bombing runs by a pair of Tupolev Tu-160 heavy strategic bombers on Thursday, a training exercise of the countries’ joint air defence systems. “Let them squeak and shout,” Lukashenko told his top officials in bellicose remarks. “Yes, these are bombers capable of carrying nuclear weapons. But we have no other option. We have to see what they are doing beyond the borders.” Lukashenko also claimed that there had been attempts to smuggle weapons from east Ukraine to those on the border in an attempt to “provoke our border guards into a conflict with theirs”. He did not provide any evidence for the claim, which he said he had discussed with Vladimir Putin. Ukraine’s interior ministry on Thursday announced that it was planning to deploy an additional 8,500 troops and police officers, as well as 15 helicopters, to prevent attempts by people to cross the border. Although not part of the EU, the country has said it is also concerned at being drawn into the crisis. European officials said that they expected the crisis to worsen. The German foreign minister, Heiko Maas, said that the picture from the border camps between Belarus and Poland were “terrible”. “Lukashenko is responsible for this suffering. He abuses people to put the EU under pressure.”