Opposition parties have questioned why the Scottish Government "kept quiet" about a multi-billion pound investment agreement with Chinese companies signed in March.

SNP leader Nicola Sturgeon signed a memorandum of understanding with SinoFortone and China Railway No 3 Engineering Group before the Scottish Parliament was dissolved on March 24.

Investment company SinoFortone said the agreement will bring about infrastructure projects with a potential value of £10bn in areas including clean energy, transport and affordable housing.

The group's website features pictures of Ms Sturgeon joined at Bute House by managing director Dr Peter Zhang, Sir Richard Heygate, senior adviser for China Railway No 3 Engineering Group, and Consul General Pan Xinchun.

Scottish Labour said details of the deal only emerged after they were reported by Chinese media.

Following media reports on Sunday, the Scottish Government published the agreement document on its website.

Public services spokeswoman Jackie Baillie called for the full facts to be published without delay.

Ms Baillie said: "Voters deserve the facts on deals the SNP Government have signed on their behalf and it is unacceptable to refuse to tell people what is in this deal.

"It simply isn't good enough to blame the purdah election period. The SNP signed this deal before that but kept it quiet - people deserve to know why."

Scottish Liberal Democrat leader Willie Rennie said: "It is extraordinary that a deal of such magnitude has been kept private by the SNP.

"What have they got to hide that they signed this covert agreement with the Chinese when parliament was unable to scrutinise it?

"We need to know what the SNP have signed up to. What have they given in return for this investment?" Scottish Conservative chief whip John Lamont said:

"Why did the SNP keep this under wraps, and why was Parliament not informed?

"It appears as if the SNP simply tried to hide this away until after the election. It's not good enough - Nicola Sturgeon must now set out exactly why this has only come to light now."

Quoted on the SinoFortone website, Ms Sturgeon said: "We have been co-operating and engaging with China since 2007 and I further progressed Scotland's business credentials during my trip last year, and this Memorandum of Understanding will strengthen our economic links with China in a number of areas.

"New innovation collaborations between Scotland and China can deliver a boost in business growth for both countries and deliver benefits to Scotland as a whole.

"We have high hopes for Scotland's economy and it is in a strong position, but if we can drive further growth by looking beyond our shores and building relationships with firms across the world, then we will seek to make that happen."

Consul General Pan Xinchun said the agreement will benefit "not only Chinese enterprises but also the Scottish people".

Businessman Sir Brian Souter was also quoted on the SinoFortone website.

He said: "It is a very positive step for Scotland to attract investment of this nature.

"SinoFortone's investment will be good for our economy, create jobs and enable growth. We look forward to hearing more about the specific projects and infrastructure that they are aiming to invest in."

Ms Baillie said: "It simply isn't acceptable that a millionaire SNP donor knows the details of this deal but the people of Scotland don't."

An SNP spokesperson said: "The First Minister is more than happy for this information to be in the public domain which shows that once again opposition parties are ignoring reality to make up their own version of events - a move which has backfired badly.

"As the Memorandum of Understanding, which the Scottish Government has published, clearly shows it is an agreement to have preliminary talks about potential opportunities for investment to support jobs and economic growth in Scotland. It does not relate to any specific projects or specific amount of investment, is not a binding legal agreement and does not commit any public funds.

"It is the job of government to secure appropriate investment for Scotland and to do what we can to boost the economy, as we have done in the case of Ferguson's shipyard and most recently when the SNP Government stepped in to secure a future for the Tata steel works in Dalzell and Clydebridge."