A train drivers' union has called for transport minister Humza Yousaf to be sacked.

ASLEF, which represents nearly 20,000 UK drivers, called on the First Minister to take "personal responsibility" after a morning of chaos on the railways and sack Mr Yousaf.

The union issued a statement on Thursday evening branding the SNP transport minister "incompetent" and said Nicola Sturgeon should relieve him of his ministerial duties.

They also called for ScotRail, currently operated by Dutch firm Abellio, to be returned to public ownership.

The comments follow an incident on Thursday when a train broke down near Princes Street Gardens during rush hour causing misery for tens of thousands of commuters.

ASLEF said it was "simply the latest example of poor performance from an Abellio Scotrail service which goes from bad to worse".

General secretary Mick Whelan said: "The Scottish Government response to the rail crisis has been pathetic.

"Transport minister Humza Yousaf has stood by while Abellio ScotRail takes Scotland's passengers and taxpayers for a ride."

He added: "Nicola Sturgeon must take personal responsibility for this situation as her government awarded this contract.

"She should sack her incompetent transport minister. You can't control what you don't own so the Scottish government should do the decent thing and return the railway to public ownership."

Responding to ASLEF's comment, a Scottish Government spokesman said ScotRail's performance was being closely monitored.

He said: "As ASLEF are well aware, having met Ministers as recently as last week, we are making the best of a rail industry system imposed by the UK Government which successive UK Labour governments failed to change.

"The Labour UK Government chose not to stop franchising either in the Transport Act of 2000 or Railways Act of 2005.

"We pressed all Secretaries of State in the UK Government - each refused, the last in 2012 forcing us to go ahead with tendering process. We were left with no alternative but to embark on a commercial procurement exercise, and we did so.

"We are now committed to ensuring the success of the current rail franchise contracts we have let. Using the additional rail powers that are being provided through the Scotland Act, which allow public sector bodies to bid for future Scottish rail franchises, we will deliver on our manifesto pledge to ensure a public sector body is in position should either the Scottish Government or ScotRail take steps to invoke the break-point in the current contract, which would end the franchise after seven years (April 2022, but decided by March 2020).

"ScotRail's Performance, as we all know, is being tracked closely by passengers, government and the media, indeed Mr Yousaf is monitoring ScotRail operations this evening and early tomorrow to see and hear how they are tackling performance issues.

"Currently 89 out of 100 trains achieve the contracted performance measure, this is around 2% ahead of the GB average.

"We expect Scotrail to improve on their performance, as per their contractual obligations. As the First Minister said, if performance does not improve the Scottish Government keeps all options on the ‎table‎"

Earlier in the day, Nicola Sturgeon vowed to cancel Abellio's contract if the performance of the network didn't improve.

During a heated exchange at Holyrood, the First Minister apologised to rail passengers and raised the prospect of using a break clause in its contract with Abellio to bring ScotRail out of its hands five years earlier than expected.

"There are options for the contract to be broken early and we will keep that option under review," Sturgeon said.

ScotRail has since launched an internal review into the way the incident was handled after it was heavily criticised for a lack of communication.

Phil Verster, managing director of the ScotRail Alliance, said: "I want to apologise for the disruption our customers experienced today.

"The breakdown this morning was the worst type of train failure, in the worst part of our network at the worst possible time.

"We worked hard to get information to our customers as quickly as possible - through social media, our website and app and at our stations."

The Scottish Government has been contacted for a response.