The chairman of Oxfam International, Juan Alberto Fuentes, has been arrested as part of a corruption investigation in Guatemala, according to the public prosecutor's office.

The country’s former president, Alvaro Colom, has also been detained in the probe.

"One of the ten people detained in today's operation is the ex-president of the republic, Alvaro Colom," Juan Francisco Sandoval, chief anti-corruption officer at the public prosecutor's office, said on local radio.

Mr Fuentes, a former finance minister who is currently chairman of Oxfam International, was also among those arrested, prosecutors said.

His arrest ratchets up the pressure on the British charity, already reeling after reports of sex abuse by aid workers in Haiti.

Mr Colom, 66, was president of Guatemala from 2008 to 2012.

The corruption investigation is looking at buses bought during his administration for a large public transport programme.

"We think everything was legal, but let's wait and see what the judge says," Mr Colom said as he entered the courthouse.

The eight other people arrested were Mr Colom's former ministers who signed the deal to purchase the buses.

Mr Colom is not the first Guatemalan leader to face corruption accusations.

Current President Jimmy Morales, a former television comedian who ran on an anti-corruption ticket, came under fire last year from the United Nations, the European Union and the US ambassador in Guatemala for attempting to expel a UN-backed prosecutor seeking to put him on trial for alleged corruption.

The investigation into allegations of illicit campaign financing, which followed separate corruption investigations into members of the president's family, had threatened Mr Morales with impeachment.

He escaped that fate but his authority has been seriously hampered.

Mr Morales' predecessor, former president Otto Perez, is currently behind bars, awaiting trial on corruption charges.