Pentagon spokesman Lt Col Koné Faulkner said the US military would aim to spend the money on other “urgent priorities”.
The move, which needs to be approved by US Congress, is part of a broader suspension announced in January.
The US state department has criticised Pakistan, a key ally, for failing to deal with terrorist networks operating on its soil, including the Haqqani network and the Afghan Taliban.
“We continue to press Pakistan to indiscriminately target all terrorist groups,” Col Faulkner said in a statement on Saturday, adding that the $300m aid – which had earlier been suspended – should be used elsewhere due to “a lack of Pakistani decisive actions” in tackling the issue.
The announcement comes just days before US Secretary of State Mike Pompeo is due to visit Pakistan.
In January, the US government announced it was cutting almost all security aid to the country.
The US and others have long complained that Pakistan provides a safe haven to militant networks, allowing them to carry out cross-border attacks in Afghanistan – something that Islamabad denies.
Separately on Friday, the US said it was ending all funding for the UN’s Palestinian refugee agency – the United…