BOGOTA, Nov 18 (Reuters) - Net profit at Colombia's Grupo Aval was down 2.5% in the third quarter to 1.21 trillion pesos ($309.6 million) compared to the same period a year earlier, the conglomerate said on Thursday.

The fall in net profit was partly explained by an increase in tax rates under a reform approved recently by Congress, the company said in a statement.

Income from interest was down 2.6% in the third quarter to 4.97 trillion ($1.27 billion) compared to the same period the year before.

Compared to the second quarter, net profit was down 29.4%. Profit attributable to shareholders was up 12.9% between July and September to 779.7 billion ($199.5 million) or 35 pesos per share when compared to the same period in 2020.

Grupo Aval includes banks Banco de Bogota, Banco Popular, Banco AV Villas, Banco de Occidente, Corporacion Financiera Colombiana and pension fund Porvenir.

($1 = 3,907.95 Colombian pesos) (Reporting by Nelson Bocanegra Writing by Julia Symmes Cobb Editing by Chris Reese)