Donald Trump’s efforts to pile pressure on North Korea have provoked a backlash over the border in South Korea, where confusion is turning to consternation at the US president’s rhetoric and brinkmanship.

A political vacuum following the downfall of President Park Geun-hye has left Seoul, one of Washington’s closest allies, marginalised from discussions on North Korea and the nuclear threat it poses, while US messaging on the deployment of an aircraft carrier strike force has undermined confidence.

“There is a lot of vacillating from Washington and that puts gas on any potential fires,” said Song Min-soon, a former South Korean foreign minister. “If it continues, it could be serious — not only for anti-US sentiment, but for the whole US-Korea alliance.”