An oil rig carrying 280 tonnes of diesel has run aground after being blown ashore in severe weather conditions.

The drilling rig Transocean Winner is being monitored by a counter-pollution team after grounding on the western side of the Isle of Lewis in the Western Isles.

The semi-submersible rig became detached from its tug during a towing operation in the early hours.

Severe weather including high winds prevented the crew of the Alp Forward from reconnecting the tow line.

No-one was on board the rig when it grounded near Carloway, the Maritime and Coastguard Agency said.

A spokeswoman said: "The Maritime and Coastguard Agency's counter-pollution branch and the Secretary Of State's Representative for Salvage and Intervention (SOSREP) have both been monitoring the situation since Sunday evening and the local authority, police and Marine Scotland have all been kept informed.

"There is 280 metric tonnes of diesel on board and this situation is being monitored. SMIT Salvage has been mobilised to deal with the incident."

Local politicians have united in a call for an emergency towing vessel to be reintroduced for the Western Isles.

SNP MP Angus MacNeil campaigned on the issue after the previous emergency tow was removed.

He said: "Thankfully we have been hearing today there have been no casualties involved as no personnel were on board the rig at the time.

"However, this could have been a very different outcome, and it is another example of why we need to have an emergency towing vessel on the west coast of Scotland. The UK Government must return the ETV to Stornoway - a tug is an insurance policy for an unusual but possible event.

"I am also calling on the UK Government to carry out an immediate investigation as to why this oil rig was being towed in severe winds west of the Hebrides, and I'm seeking further details regarding the response time - which the Maritime and Coastguard Agency has said took 18 hours."

Highlands and Islands Labour MSP Rhoda Grant said: "The one remaining emergency tug that covers the north and west coast is based in Orkney and takes an estimated eight hours to reach the north Minch and a staggering 12 hours to reach Barra Head from its Orkney base.

"Just two days after the tug was removed from Stornoway in March 2012, a cargo ship ran aground on North Uist. There was no loss to life on that occasion either, fortunately, but we cannot simply rely on good fortune to protect staff, passengers and our environment from any future disasters."

Scotland's Environment Secretary, Roseanna Cunningham, said: "We are in close contact with the UK Government - which is responsible for managing the response - as well as the emergency services and the Maritime and Coastguard Agency regarding this incident.

"They are working to ensure the rig is secured and to minimise any immediate safety or environmental risks.

"The environment group which has been set up under the UK National Contingency Plan is chaired by Marine Scotland and will continue to monitor the on-going situation."