The Scottish government has asked the harbour authority Forth Ports to freeze plans for ship-to-ship oil transfers in the Firth of Forth.
The oil would be transferred in the Firth of Forth
Environment Secretary Richard Lochhead wants to hold talks with Westminster on new legislation giving ministers powers to block such proposals.
Mr Lochhead also raised concern that Forth Ports was "judge and jury" of its own assessments.
But he said the company had given environmental assurances.
Forth Ports has the final say on controversial proposals from SPT Marine Services to pump about 7.8 million tonnes of Russian crude oil a year between tankers anchored four miles off the coast.
Local authorities on both sides of the estuary have voiced opposition to the scheme.
In a statement to the Scottish Parliament, Mr Lochhead said the Firth of Forth, several parts of which have special protection status, had to be safeguarded.
"The message from communities on all sides of the Forth has been one of concern," he said.
Mr Lochhead said he would make representations to the UK Government on whether or not powers should be exercised to stop the proposal, and how those powers should be transferred to the Scottish Parliament.
But former Labour environment minister Rhona Brankin branded his statement "wishy-washy".
The environment secretary said there appeared to be a strong case to rule out new ship-to-ship transfers near environmentally sensitive areas and argued that ministers should have powers to consider the merits of such proposals.
The Greens have drafted regulations which would require a certificate of compliance to be issued by ministers before the project could go ahead.
"I would ask and have asked Forth Ports not to take any precipitate action before we have had the opportunity to consider the issue in detail and as a matter of urgency," Mr Lochhead added.
He said that, to the public's "amazement", ministers were excluded from the decision-making process.
Mr Lochhead said of Forth Ports: "They are the statutory harbour authority. They are responsible for the regulation of and specific oil transfer operation in its area. They will develop the assessment of environmental impact and make the judgement on whether the proposal might damage the integrity of the environment.
"They are effectively both judge and jury of their own assessment. That cannot be right."
The transfer would involve several million tonnes of oil
Ms Brankin said her party believed that ship-to-ship oil transfer in the Firth of Forth was a step too far and that the environmental risks potentially outweighed the economic benefits.
"We in government gave a commitment to change the habitat regulations. What we have today is a wishy-washy approach which basically says this is all very difficult.
"What we have heard is a complete cop-out with no new commitments. It's simply not good enough."
Scottish Tory environment spokesman John Scott said his party was "largely supportive" of the minister's aims.
"We note concerns that have been raised about the dual role of Forth Ports Plc and believe, as the minister hinted, that a conflict of interests exists," he added.
Iain Smith, Liberal Democrat MSP for North East Fife, said concern over ship-to-ship transfers extended to all parties.
"I am sure there is cross-party support for the view that Forth Ports should not be both the commercial operator and statutory regulator on this issue," he told MSPs.
Green co-leader Robin Harper urged Mr Lochhead to take a rapid decision on whether his party's solution represented "the fastest route in a very urgent situation" for the Scottish government to gain the powers it required.
A spokesman for Forth Ports said the authority was making a "thorough and proper assessment" of the proposals, covering safety and environmental considerations.
"We carry out our duties in compliance with domestic and European legislation and we would not comment on any future legislation until it was in place," said the spokesman.
"We look forward to working with the new administration for the economic benefit of Scotland. In order to achieve this goal it is important that we are competing on a level playing field with other UK harbour authorities."