Ash from an Icelandic volcano is being blown toward Scotland, forcing one airline to cancel nearly all its flights and Barack Obama to cut short his visit to Ireland amid fears of the huge flight disruptions that stranded millions of passengers a year ago.

The U.S. president flew from Dublin to London on Monday night, leaving the Irish capital a day earlier than planned, because of concerns over the eruption of the Grimsvotn volcano, a White House official said.

Obama arrived in Ireland earlier Monday to begin a six-day European state visit.

British Airways has cancelled all Tuesday morning flights between London and Scotland due to forecasts of volcanic ash expected to move into Scottish airspace as early as Monday night.

BA said there will be no flights until Tuesday at 2 p.m. local time as a precaution.

Customers on cancelled flights will get a full refund or can be rebooked onto alternative flights.

Royal Dutch Airlines KLM cancelled more than a dozen flights to and from Scotland and northern England.

The airline confirmed on its website Monday night that 16 flights scheduled for Tuesday morning to and from Aberdeen, Glasgow, Edinburgh and Newcastle were cancelled.

Glasgow-based regional airline Loganair cancelled 36 flights scheduled for Tuesday morning. It said its flights between Scottish islands would be unaffected.

Officials in Iceland closed the country's main airport, Keflavik International in Reykjavik, after Grimsvotn erupted on Saturday, but said they would resume flights later Monday.

Britain's Met Office predicted the plume would move over Ireland, Scotland and parts of northern England by Monday evening or Tuesday morning.

A spokesman for the U.K.'s Civil Aviation Authority said it's likely some flights would be disrupted.

Aviation officials in Norway said the cloud might also affect flights to and from the Arctic islands of Svalbard on Monday.

Volcanic ash can pose a threat to aircraft engines if it melts inside the engine's combustion chamber. The molten ash can coat the turbine blades and disturb the normal air flow. 

Danish air traffic officials said the main ash plume had reached eastern Greenland and Air Greenland said its Monday flight between the island's main airport and Copenhagen was cancelled as a result.

Iceland  shut down Keflavik airport  after the volcano started erupting on the weekend for the first time since 2004, but an Icelandic meteorological official on Monday said the eruption — 200 kilometres east of Reykjavik — already appears to be getting smaller.

In April 2010, another volcanic eruption grounded planes across northern Europe for five days, stranding some 10 million travellers. Thousands of flights were grounded and airlines lost millions of dollars after the Eyjafjallajokull volcano blew.

Because of what happened last year, British government officials say they are now better prepared to avoid a mass grounding of planes under similar circumstances with new guidelines that can determine which airline fleets are safe enough to fly through low- and medium-density ash clouds.

It  was not immediately clear how many flights, if any, could be disrupted by the Grimsvotn eruption. Although the wind is blowing it westward, experts say the ash could be far enough north to be clear of most flight paths.

The plume could be over parts of France and Spain by Thursday or Friday if the eruption continues at the same intensity, airlines have been warned.

The warning is based on the latest five-day weather forecasts, but is being treated cautiously because of uncertainties over the way the volcano will behave and interact with the weather.

With files from The Associated Press