UPDATE 1-Maybank may raise as much as $1.63 bln - sources

* may raise up to 6 bln ringgit via rights sale - sources

* Goldman, Credit Suisse hired for rights offering

* rights share sale seen around April (Adds timing, background)

HONG KONG, Feb 24 (Reuters) - Malayan Banking Bhd (MBBM.KL), Malaysia's biggest lender, plans to raise 5-6 billion ringgit ($1.36-$1.63 billion) through a rights offering, banking sources said on Tuesday, up to double what it initially said it may raise to boost its working capital.

Analysts have said Maybank's Tier-1 capital ratio could drop to below 8 percent by the year-end due to writedowns linked to its acquisition of Bank Internasional Indonesia (BNII.JK), and that it may issue shares to shore up its balance sheet.

Maybank said last month it was looking at various options for raising the funds.

The sources said Goldman Sachs and Credit Suisse have been hired to arrange the rights offering. The sources, who were not authorised to speak on the record, did not say why Maybank was planning to raise a larger amount.

A source with direct knowledge of the deal said Maybank may target the rights share sale around April.

Maybank's move comes after Singapore's DBS Group (DBSM.SI), Southeast Asia's biggest lender, in January raised S$4 billion through a rights share offering.

Tay Chin Seng, a banking analyst at Macquarie Securities, said Maybank needed capital as part of funding for the $2.2 billion acquisition of BII, but he does not see large equity fund raising in the region.

"Most of the Southeast Asian banks do not seem to be looking for equity, rather they want to augment their Tier-1 with hybrids," he said. "I don't see an avalanche of equity capital raising in the region."

Maybank, Goldman Sachs and Credit Suisse all declined to comment. (Reporting by Michael Flaherty in HONG KONG and Saeed Azhar in SINGAPORE, Editing by Ian Geoghegan)