(Reuters) -Australia's Westpac Banking ( WEBNF ) posted a 13% rise in its first-quarter net profit on Monday, helped by growth in customer deposits and housing and business loan volumes.

The country's No. 3 lender by market value said unaudited net profit was A$1.7 billion ($1.08 billion) for the three months ended December 31, compared with A$1.5 billion posted a year earlier.

The bank's core net interest margin - the difference between interest earned from lending and paid for deposits - fell 2 basis points from the second half of last year to 1.81%.

"The modest decline reflects prudent management in the context of ongoing mortgage competition and further deposit mix shift towards lower spread savings and term deposits," Westpac said in a statement.

($1 = 1.5748 Australian dollars)