Ryanair, Europe's largest low-cost airline, on Monday offered to buy Irish rival Aer Lingus for 750 million euros ($970.4 million) or just half the price of its bid in 2006 which was blocked by the European Union.

Ryanair, which already owns 29.82 percent of Aer Lingus, said the all-cash offer at 1.40 euros per share represented a 28 percent premium over the closing price of Aer Lingus shares for the 30 days to 28 November 2008.

A spokeswoman for Aer Lingus, which strongly opposed Ryanair's last offer, declined to comment.

Ryanair's chief executive, Michael O'Leary, told broadcaster CNBC the economic and regulatory environment had changed markedly since Ryanair's last move on Aer Lingus was thwarted by the regulatory authorities.

"It (Aer Lingus) is increasingly viewed as a small, peripheral airline that has been bypassed by EU consolidation," he said. "I think that without this bid Aer Lingus will continue to be isolated and loss making."

For its latest bid to succeed Ryanair would also have to overcome opposition from the Irish government and Aer Lingus employees who both own stakes in the airline and rejected Ryanair's last offer.

O'Leary said he believed Aer Lingus staff would be more welcoming this time round given job losses at the airline over the last two years.

Ryanair said in its offer document that it would double the size of Aer Lingus's short haul fleet to 33 from 66 over the next five years, creating 1,000 new jobs at the former state airline.

Shares in Aer Lingus jumped almost 22 percent in London to 1.36 euros by 0819 GMT, just under the Ryanair offer price.

Ryanair's shares were down 0.3 percent in Dublin at 2.92 euros, while the wider Irish market was up 0.6 percent.