The operation to free a stricken oil rig from the Western Isles has caused no water pollution so far, according to experts.

The Transocean Winner was carrying 280 metric tonnes of diesel, around 300,000 litres, when it ran aground on the western side of Lewis on August 8.

Two of its four fuel tanks were damaged in the incident, resulting in the loss of up to 53,000 litres of fuel, sparking fears of marine pollution.

Most of the leaked diesel is thought to have evaporated without causing any significant threat and an operation to remove the remaining fuel continues.

The semi-submersible remains at Dalmore beach on the western side of the island after it was blown ashore in severe weather when it detached from its tug en-route from Norway to Malta.

A Maritime and Coastguard Agency spokeswoman said on Friday: "Transocean has confirmed they started the operation yesterday to remove some of the diesel oil in the pontoon. This will continue today.

"A verification flight by the Maritime and Coastguard Agency's counter-pollution team has been carried out following that work and there is no evidence of pollution in the area."

A public meeting was held on Thursday evening at nearby Carloway, where various officials updated residents on the salvage operation.

The meeting was told good progress is being made in the operation to refloat the structure, but it remains "tricky to predict" when that can actually take place.

Dave Walls, operations director with Transocean, thanked the community and emergency services for their help.

"The other thing I would like to do is to apologise for the disruption to your daily lives," he said.

Mr Walls said much has already been accomplished by the 15 people who are now working aboard the rig, with emergency generators, pumps and internal cameras among the systems already up and running.

With the compressors needed to refloat the structure set to arrive on the island by ferry on Friday, officials cannot yet state when the rig will actually be removed from the beach.

Mr Walls said: "We need to get ourselves in the position where we're ready to float and we're not there yet.

"Once we're ready to float we then need the ideal conditions to float - and that's a suitable weather window, no wind, the right tide.

"Everything needs to be just right because we get one opportunity to do it right."

He vowed no trace of the rig would be left when the salvage operation - including a sweep of the seabed - is complete.

A Marine Accident Investigation Branch investigation has been launched into the incident.