Britain has sent a team of about 10 soldiers to Poland to help Warsaw strengthen its border with Belarus, where groups of migrants have been stranded attempting to cross into the EU. The troops arrived on Thursday and are expected to spend a few days in the country, including visiting the border at the request of the Polish government to work out if they can repair or toughen the fencing. The Ministry of Defence said the mission was focused only on “engineering support to address the ongoing situation at the Belarus border”, and insiders said there was no additional plan for British troops to police the border. Whitehall sources said was appropriate to consider helping Poland given that “it is Belarus that is pushing migrants towards the border”. Any final decision to help will have to be signed off by the defence secretary, Ben Wallace. Hundreds of people are stranded in camp on the Belarus-Poland border in near-freezing temperatures, having been allowed to fly from Iraq, Turkey, and elsewhere in the Middle East in a growing humanitarian crisis. Poland has established a state of emergency in the border region enforced by 20,000 border police is refusing to allow them in. But while Warsaw has asked for British help, it has refused help from the EU’s Frontex border management agency. It is not clear why Poland feels it needs British engineering assistance, but the two countries have become close as each is engaged in disputes with the EU. At the end of October, Boris Johnson spoke to the Polish prime minister, Mateusz Morawiecki, about his concerns over the influence of the European court of justice over the Northern Ireland protocol. Poland is embroiled in a separate row with the EU over the primacy of the ECJ after its constitutional court ruled that Polish law supersedes EU law where there is a conflict between the two. Britain had been planning to announce the mission next week in conjunction with Warsaw, but news of the deployment leaked. It was then confirmed on Twitter by the Polish defence minister, Mariusz Błaszczak, who said the aim was “to cooperate in strengthening the [border] fence”. The MoD said: “The UK and Poland have a long history of friendship and are Nato allies. A small team of UK armed forces personnel have deployed following an agreement with the Polish government to explore how we can provide engineering support to address the ongoing situation at the Belarus border.” Human rights groups criticised the move, arguing that the UK should concentrate on alleviating the humanitarian crisis. Steve Valdez-Symonds, Amnesty International UK’s refugee and migrant rights director, said: “Sending British soldiers to erect more border fences rather than address the needs of people dying at those borders shows a shocking disregard for both human life and the right of people to seek asylum.” Poland has accused Russia of behind the migrant crisis by encouraging Belarus to send people to the border. This week Morawiecki said the actions of Belarus, which is subject to EU sanctions after the dispute re-election of its leader Alexander Lukashenko, “has its mastermind in Moscow”. There have been other tensions in the east, with the US sharing intelligence with European allies about Russia’s military buildup along the Ukrainian border. Despite the military deployment, the US believes that Vladimir Putin has not as yet made a decision to invade. However, that assessment – that Putin is using the buildup of troops primarily to put pressure on the government in Kyiv – is not unanimously shared, and some US agencies are more concerned than others about the imminence of another Russian incursion, according to sources familiar with the discussions. “There are some parts of the administration who are less concerned and see it as more of the same, Moscow destabilising Ukraine by moving troops around, and others who are very worried, who see it as something different from before,” said a European official. The Ukrainian president, Volodymyr Zelensky, has been warning for months about the presence of up to 100,000 Russian troops in the border region. Moscow withdrew some troops after exercises in April but then sent more soldiers back after the summer for more war games in September. This time it left the additional forces in place. This month Ukraine’s defence ministry estimated the Russian force at 90,000, and commercial satellite imagery shows that Russian tank and artillery units have moved close to the border over the past month. The issue was high on the agenda of a meeting between US undersecretary of state Victoria Nuland and the political director of the UK Foreign Office, Tim Barrow, in Washington this week. The CIA chief, William Burns, flew to Moscow, last week to warn Russian security officials against any further escalation, and officials said Moscow had been marginally more cooperative since that visit. Ukraine’s foreign minister Dmytro Kuleba visited Washington this week to brief the Biden administration on the situation, and signed a new bilateral charter on strategic partnership with US secretary of state, Tony Blinken, on Wednesday. Blinken said the charter “affirms the United States’ unwavering commitment to Ukraine’s sovereignty and territorial integrity”. He said: “We’re concerned by reports of unusual Russian military activity near Ukraine. We’re monitoring the region very closely, as we always do, we’ll continue to consult closely as well with allies and partners on this issue.” Kuleba told ABC News: “We are extremely worried, but listen – when you live next to Russia for seven years in an armed conflict, you kind of learn to be worried. You get used to it.” At a summit between Zelensky and Joe Biden in September, the US promised to step up cyber and intelligence support to Kyiv. Russia covertly sent troops and military hardware across the border in 2014 in support of Russian separatists, and annexed the Crimean peninsula. The Kremlin spokesperson Dmitry Peskov rejected fears of a second invasion. “Such headlines do nothing more than pointlessly and groundlessly fuel tensions. Russia does not pose a threat to anyone,” Peskov said. “We have repeatedly said that the movement of our armed forces on our territory should not be a cause for concern.” The Russian military accused the US of provocative manoeuvres in the Black Sea, pointing to overflights by Nato reconnaissance aircraft and patrols by US warships. “We regard the aggressive US military activity in the Black Sea region as a threat to regional security and strategic stability,” the military said in a statement.