US Airways Group Inc. announced Wednesday it had raised its offer by almost 20 percent to 10.4 billion dollars to merge with Delta Air Lines Inc.

"The increased offer is set to expire on Feb. 1, 2007" unless creditors indicate support for the start of the due diligence process, which would open up Delta's books to US Airways, said US Airways in a statement.

US Airways also wants Delta to postpone a Feb. 7 bankruptcy hearing involving its reorganization plan.

The six-biggest U.S. carrier' new offer was 1.7 billion dollars higher than its 8.7 billion-dollar bid announced Nov. 15, last year.

The new offer includes 89.5 million shares of US Airways stock and 5 billion dollars in cash. The original bid included 78.5 million shares and 4 billion dollars in cash.

Delta, the third-largest U.S. carrier, has said that is opposes a buyout by US Airways. It has filed a reorganization plan that calls for it to emerge from bankruptcy by the middle of this year as a standalone company.

In a plan to exit bankruptcy, managers at Delta Air Lines on Dec. 20 valued the carrier at 9.4 billion to 12 billion dollars and said its board had rejected US Airways' 8.7 billion dollar bid.