US intelligence reportedly warned in February that Ukraine might fail to amass sufficient troops and weaponry for its planned spring counter-offensive, and might fall “well short” of Kyiv’s goals for recapturing territory seized by Russia, according to one of a trove of leaked defence documents. A document tagged as “top secret” quoted by the Washington Post said that Kyiv was facing significant “force generation and sustainment shortfalls” and was therefore only likely to achieve “modest territorial gains”. The document is a snapshot of the situation in early February, and it is unclear how far Ukraine, with the support of Nato member states, has been able to make up the shortfalls since then. Another document, dated 23 February and seen by the Guardian, gives an overview of the progress of building 12 “combat credible” new brigades to lead the counter-offensive, equipped with a target of 253 tanks and about 1,500 other armoured vehicles of different kinds. Three brigades were to be generated by the Ukrainians alone, while the remaining nine were to be established with the help of the US, allies and partners. The planned brigades were a long way from readiness at the time of the documents, with five yet to begin their training. Six of the brigades had half or less the equipment they needed to hand. The White House would not officially confirm the authenticity of the documents, but US officials have so far only pointed to one document about Russian and Ukrainian casualties, reposted on the Telegram messaging app, as having been manipulated. The justice department has begun a criminal investigation into the leak, and the Biden administration has confirmed it is talking to partners to limit the damage to a string of bilateral relations. “We will continue to investigate and turn over every rock until we find the source of this and the extent of it,” the defence secretary, Lloyd Austin told reporters on Tuesday. Kyiv has yet to comment officially on the leaks, which laid bare Ukraine’s military deployments along the frontlines and their vulnerabilities, especially in the form of depleted stocks of ammunition. “The US is their biggest backer, so they [Ukraine] will get over it,” one European diplomat said. “The US have been consistently downbeat on Ukraine’s capabilities and they keep on getting it wrong. So that’s not new. What is damaging is it reveals what the Americans do and do not know about the Russians. And that’s a problem.” NEW“The other big problem is we don’t know how much is out there,” the diplomat said. ENDNEW The leaked documents also revealed fraught relations with supposed allies and partners, including some who appear to lean more towards Moscow. One of the documents, drawn from CIA intelligence reports, show that the Hungarian prime minister, Viktor Orbán, described the US as one of the top three adversaries of his party, Fidesz, at an internal political strategy session on 22 February. The discussion took place at a Fidesz parliamentary group meeting in Balatonfüred. A pro-government source in Budapest claimed Orbán had not named the US but the Biden administration specifically as a top adversary, arguing that constituted an “important difference”. The source added: “Members of Fidesz feared the US government would interfere in the election in some way.” NEW A Budapest-based diplomat said: “The relationship between the United States and Hungary has never been so tense before”ENDNEW The disclosure of the highly classified material represents Washington’s worst national security breach in many years, and includes details about Ukraine’s lack of ammunition and US intelligence-collection methods used against Russia. One of the latest leaks claims Egypt was planning to covertly supply Russia with rockets and other munitions, although the US was said to believe the plan had never been carried out, the Washington Post reported. “Egypt is a significant security partner and remains so in the region,” John Kirby, the national security council spokesman, said. He would not comment on the authenticity of the documents but added: “What I will tell you is we’ve seen no indication that Egypt is providing lethal weaponry capabilities to Russia.” Asked about the document, the spokesperson for Egypt’s foreign ministry, Ahmed Abu Zeid, told the Post: “Egypt’s position from the beginning is based on non-involvement in this crisis and committing to maintain equal distance with both sides, while affirming Egypt’s support to the UN charter and international law.” The unverified documents relating to South Korea, including some apparently based on internal discussions among top South Korean security officials, claimed Seoul was concerned that artillery shells bound for the US could eventually find their way to Ukraine. The possibility that South Korean weapons could be used by Ukraine would be deeply problematic for the president, Yoon Suk-yeol, as it would violate the country’s longstanding policy – supported by a majority of voters – of not exporting weapons to countries at war. On Tuesday, however, officials attempted to play down the significance of the Pentagon documents, whose authenticity has not been independently confirmed. Yoon’s office said an initial investigation had concluded there was “little chance” that internal discussions had been intercepted by US intelligence officials, the Yonhap news agency said. Kim Tae-hyo, South Korea’s deputy national security adviser, claimed the information reportedly gleaned from internal discussions was “untrue” and had been “altered”. “The two countries have the same assessment – that much of the information disclosed is altered,” Kim told reporters as he left for Washington in advance of Yoon’s visit to the US at the end of the month. The undated document in question said South Korea had agreed to sell artillery shells to help the US replenish its stockpiles, insisting that the “end user” should be the US. But it added that senior South Korean officials were worried that Washington would divert the shells to Ukraine. Austin spoke to his South Korean counterpart on Tuesday as officials in Seoul denied the possibility that the president’s office could have been the source of leaks about South Korean arms sales to the US. Kim said speculation that the US had been spying on South Korea – a key ally and host to 28,500 US troops – would not harm bilateral ties. “The US is the country with the world’s best intelligence capabilities, and since [Yoon’s] inauguration we have shared intelligence in almost every sector,” he said. The chief of the Australian Defence Force, Gen Angus Campbell, described the alleged leaks as potentially damaging, and said their dissemination could undermine trust between allies.