Aviation chiefs said airspace over Scotland and Northern Ireland would be closed Wednesday as more ash is spewed from an Icelandic volcano that caused air travel chaos in Europe last month.

The news came shortly after a flight ban imposed in Ireland, Northern Ireland and western Scotland for several hours was lifted on Tuesday, raising hopes for passengers that the return of the ash may have been brief.

But just hours later Britain's Civil Aviation Authority (CAA) ordered a new airspace closure from 7:00 am (0600 GMT) the following day, saying the levels of ash in the skies could prove dangerous for jet engines.

"Forecasts show that levels of ash in the atmosphere over Scotland and Northern Ireland will exceed the concentrations that engine manufacturers have agreed are safe for operations," said the CAA in a statement Tuesday.

"Unfortunately, this means that the CAA anticipates all Scottish and Northern Ireland airports will be closed from 07:00 local time (Wednesday)."

According to meteorologists, the cloud over Britain had "increased in density as ash emissions from the Icelandic volcano... have become stronger," said the air watchdog.

The CAA gave no indication of when the ban would be lifted and warned the cloud may float further south and close airports in northwest England and Wales on Wednesday.

Airspace across Europe was closed for up to a week last month after the eruption of Iceland's Eyjafjoell volcano, but was re-opened after emergency talks between European governments, airlines and regulators.

The return of the ash cloud led to the CAA closing airspace from late Monday over the Outer Hebrides, a group of islands off Scotland's west coast, before grounding flights in and out of Northern Ireland for several hours early Tuesday.

The Irish Aviation Authority also grounded flights into and out of Ireland early Tuesday.

Both air authorities cleared flights to resume from 1:00 pm (1200 GMT), before the latest restrictions for Wednesday were announced.

The first ban prevented thousands of travellers from flying -- including the Irish Transport Minister Noel Dempsey, who was due in Brussels for EU talks on last month's chaos.

The alerts early Tuesday did not disrupt aircraft flying over Ireland from Britain or Europe, or southern British airports including Heathrow, Europe's busiest air hub, authorities in the two countries said.

But they triggered the cancellation of hundreds of flights in and out of Ireland and Northern Ireland, bringing fresh chaos to thousands of air travellers.

In Reykjavik, experts said the new airport closures were due to a small, temporary hike in ash from the volcano at the weekend along with a change in wind direction.

"The ash plume temporarily increased a little on Sunday, but now it has decreased," Bryndis Brandsdottir, a geophysicist at the University of Iceland, told AFP.

Meanwhile Irish airline Aer Lingus said the flight ban last month had cost it about 20 million euros (26 million dollars), while warning that "the final cost will depend on the actual level of customer claims."

The Association of British Insurers estimated Tuesday that the travel chaos caused by the ash had cost insurers around 62 million pounds (94 million dollars, 72 million euros).

Eurocontrol, the continent's air traffic control co-ordinator, said more than 100,000 flights to, from and within Europe had been cancelled between April 15 and 21, preventing an estimated 10 million passengers from travelling.

burs/sr/br