(Adds comment from central bank in paragraph 3)
By Guillermo Parra-Bernal and Aluísio Alves
SAO PAULO, Aug 14 (Reuters) - State-run Caixa Econômica Federal SA won approval from Brazil's central bank to book 28 billion reais ($12.4 billion) in hybrid securities as common equity, a move that should help allay capital concerns at the nation's No. 1 mortgage lender.
With the central bank's approval, Caixa's regulatory capital ratio - the amount of capital that regulators require a bank to hold - could jump by 1.3 percentage points, Chief Financial Officer Márcio Percival said in an interview on Thursday.
The ratio reached 13.3 percent at the end of the second quarter, above the central bank's minimum 11 percent ratio.
The central bank did not have an immediate confirmation of Percival's comments. Reuters reported on July 22 that the central bank was close to approving the plan.
The so-called hybrid instruments stemmed from capital injections made by the National Treasury, Caixa's controlling shareholder, in 2009 and in 2013. The central bank had already agreed to allow Caixa to record the securities as capital under the implementation of Basel III capital requirements, but was still deciding where on its balance sheet to book them.
Caixa's efforts come as peers in developed and emerging market countries struggle to phase in the Basel III rules, which were designed to stave off a repeat of the crisis that followed the collapse of U.S. investment bank Lehman Brothers Inc late in 2008.
Investors have voiced concerns that years of rapid growth in Caixa's loan book, fueled by the government's pressure to boost access to credit, have weighed down its capital position. The bank grew its loan book by 28 percent in 12 months ended in June, Caixa said on Thursday.
The decision allows Caixa to book the instruments as Tier 1 capital, which consists mainly of common stock, retained profits and, in some cases, non-redeemable, non-cumulative preferred stock.
Yields on Caixa's 10-year Tier 2 bond, the first of their kind to incorporate Basel III features in Brazil, slightly fell on the news to 7.224 percent, from 7.26 percent on Wednesday. Tier 2 bonds rank lower in repayment order than loans, creditor rights and other subordinated debt.
According to rules in Brazil, these type of Tier 2 bonds can be written off if a bank's common equity Tier 1 capital falls below 4.5 percent of risk-weighted assets, if the bank receives a capital injection from the government, or if the central bank decides the lender is financially unfeasible.
In recent months, central bank policymakers have announced steps such as allowing lenders to use deferred tax assets as capital to help smooth out the implementation of Basel III rules. Brazil began to implement Basel III in October. Banks must fully comply with the rules by early 2019.
$1 = 2.27 Brazilian reais Reporting by Guillermo Parra-Bernal and Aluísio Alves; Editing by Chris Reese, Bernard Orr