Powers allowing the Welsh Government to borrow millions to fund investment should not be used to build a planned M4 relief road around Newport, the Welsh Lib Dem leader has said.

By 2018 Welsh ministers will be able to borrow up to £500m and Labour plans to spend part of the money on the road.

Plans for the scheme include 24km (15m) of new motorway and a 2.5km-long (1.5m) viaduct crossing the River Usk.

But Kirsty Williams said the money should be used to build homes.

"We used our influence in the assembly to stop work on the M4. Mark my words: the Welsh Liberal Democrats would do so again," she said.

Image caption Kirsty Williams said everyone should benefit from the fund

"We will use this money to build 20,000 new homes, building them across the whole of Wales so everyone will benefit."

Economy Minister Edwina Hart told AMs last year the Welsh Government was not intending to use all the money available on a single project.

A final decision on whether the motorway scheme will go ahead will be taken after May's assembly election.