Rishi Sunak accused the SNP of “letting people down” over the failure to deliver the A9 dualling programme by 2025.
The prime minister waded into the row surrounding the long-awaited upgrade between Perth and Inverness during a visit to the north-east.
Mr Sunak said the problem had already been raised directly with him.
Scottish Secretary Alister Jack, with the prime minister on Monday, said the road is vital for the Scottish economy and pointed the finger at the Greens for delays.
On A9 dualling, Mr Sunak said: “We think having well-functioning, well-maintained roads is critical to an economy thriving and people being able to go about their day to day lives.
“That’s clearly not happening here and people are being let down by the SNP not delivering this brilliant, important transport programme.”
Greens blamed for delays
Responsibility for the road network sits at the Scottish Parliament, not the UK Parliament.
However, Mr Jack has previously pushed for the SNP to work with Westminster on road upgrades in south-west Scotland.
The Scottish Secretary said: “The A9 is the spine up through the Highlands. The SNP have failed to deal with these trunk roads.
“And they will continue to fail because the Greens, their coalition partners, are against any more roadbuilding. You need to improve your roads to improve your economy.
“Mr Yousaf needs to take a proper view of this and get behind the Scottish economy and creating more jobs in the north of Scotland and south-west of Scotland by addressing these road failings.”
I would be amazed if Rishi Sunak could pick out the A9 or A96 on a map.
– SNP Westminster leader Stephen Flynn.
Last week, the Scottish Greens said it is the “right time to look again” at the A9 dualling programme.
Mid Scotland and Fife MSP Mark Ruskell, the party’s transport spokesman, suggested roundabouts and junction improvements instead of the full upgrade.
‘Pinch of salt’
SNP Westminster leader Stephen Flynn hit back at the prime minister saying he would be “amazed” if he could pick out the A9 on a map.
He added: “I’ll take his comments with a fairly significant pinch of salt.
“There’s been significant delays in terms of the timelines around some of these projects, primarily as a result of the pandemic, but also cost pressures.
“It was Rishi Sunak and his government who crashed the economy and indeed took us out of the EU, which has led to supply shortages and a massive hike in inflation and indeed in interest rates.”
Scottish transport secretary Mairi McAllan meanwhile wrote to a prominent A9 dualling campaigner to reassure her that the Scottish Government is “resolutely committed” to the project.
The SNP minister wrote to Laura Hansler from the A9 Dual Action Group to say a new revised timetable for the scheme is being “progressed with urgency”.
First Minister Humza Yousaf previously said he is “sorry” his government has failed to meet the target to dual the road by 2025.
It was revealed earlier this year that the upgrade would no longer be completed on time.
Former transport minister Jenny Gilruth blamed economic pressures from the pandemic, Brexit and Ukraine as all having an effect on the project.
