Two Australian companies are being investigated over alleged bribery scandals linked to the presidents of Sri Lanka and the Congo, after the firms sought to secure multi-million-dollar contracts in those countries.

Key points: Sundance Resources agents allegedly involved in plot to bribe son, nephew of Republic of Congo's President

Sundance Resources agents allegedly involved in plot to bribe son, nephew of Republic of Congo's President SMEC staff involved in alleged kickback request from office of Sri Lanka President when he was a minister

A Fairfax Media and 7.30 investigation can reveal Perth's Sundance Resources is implicated in an alleged bribery plot involving some family members of Republic of Congo President Denis Sassou Nguesso.

Engineering giant Snowy Mountain Engineering Company is being separately investigated over claims its staff sought approval to pay kickbacks to foreign officials, including a donation to the party of Sri Lanka's president Maithripala Sirisena when he was a cabinet minister.

While these matters are still being investigated, the revelations place pressure on the Turnbull Government to reform Australia's maligned anti-corruption framework, and come after foreign bribery allegations implicating Tabcorp, Leighton Holdings and BHP Billiton.

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Iconic Australian firm facing bribery investigations

The office of Sri Lanka's president Maithripala Sirisena allegedly sought a political donation when he was a cabinet minister.

The iconic Snowy Mountains Engineering Company (SMEC) is the subject of a major AFP probe examining the firm's overseas operations.

7.30 can reveal SMEC's overseas staff allegedly bribed officials to secure a $2.3 million aid-funded sewerage project in Sri Lanka in 2011, and a smaller power plant project in Bangladesh in 2007.

Leaked internal company emails also reveal claims from SMEC's Sri Lankan manager in 2009 that then senior minister Maithripala Sirisena and one of his advisers allegedly requested a political "donation" before signing cabinet papers for a $1.82 million dam contract sought by SMEC. Mr Sirisena is now Sri Lanka's President.

"The minister ... wants to know whether SMEC could make a donation for the elections," an email from the SMEC manager states about his meeting with Mr Sirisena.

The same email states: "[Mr Sirisena's] Coordinating Secretary said this is the way it goes prior to signing the cabinet papers. He wants us to produce an amount/percentage on the contract value."

In a statement overnight, Mr Sirisena said he had "no knowledge of the incident" and requested further details to "ascertain the involvement of any of his office staff".

The President also said he would co-operate "in any investigation" in Australia and "will also instruct the relevant local authorities to investigate".

The SMEC Sri Lankan manager also wrote he wanted to "inform the minister/co-ordinating secretary" of the size of a suspected kickback to be paid. In another email, the manager said he needed to "prioritise" certain payments to unnamed parties "since the signing of the contract would depend" on it.

In a statement, SMEC confirmed there was a "request for a political donation".

But it said its internal investigation had found that no payment was ever made by the company in response, and the firm "continues to fully cooperate with the AFP".

The secret Congo deal

Sundance Resources agents were allegedly involved in a plot to bribe the family of the Republic of Congo President Denis Sassou Nguesso.

Sundance Resources' Mbalam‐Nabeba Iron Ore Project, on the border of Cameroon and the Republic of Congo, is touted as one of Africa's biggest iron ore ventures.

But internal Sundance files reveal an alleged plot to bribe some family members of Congo's most powerful man when the company first sought exclusive mining permits in 2006 and 2007.

A July 2006 report by Sundance's African agents states the project needed the backing of "Head of State", President Denis Sassou Nguesso.

Internal company files indicate the agents then brokered a deal potentially worth millions of dollars with the president's son and nephew for a large parcel of shares in Sundance's proposed Congo subsidiary.

"Denis Sassou Nguesso [the President's son] was delighted by the project, but clearly had a problem with the shareholders standing that was proposed to the Congolese side in this deal."

"Unless we give them [the Nguesso government] a good reason to do this project with us, they would want to … do the project with the Chinese," the confidential July 2006 report states.

The President's son was allegedly given shares worth millions of dollars. In mid-2007 his father, President Sassou Nguesso, personally signed off on Sundance's mining permits in a move Sundance's agents attributed to "our relations and network in Congo".

A Sundance spokesman told Fairfax Media the firm "has commissioned an independent party" to conduct a "thorough assessment".

The AFP said it was evaluating the case and took "these allegations very seriously".

AFP warns Australian firms

The AFP says it is ramping up inquiries and pushing companies to dob themselves in before they get caught.

"For any company to think that, you know, this is just the cost of doing business, then they are going to, in due course, face the full effect of the law," AFP Commander Peter Crozier told 7.30.

The Government gave the AFP an extra $15 million in April to fight corporate bribery after the global Unaoil bribery scandal, which involved construction giant Leighton Holdings, and allegations that Tabcorp bribed the sister of Cambodia's Prime Minister.

But experts including former NSW Supreme Court Judge and chair of NGO Transparency International Anthony Whealy say the latest revelations show far greater reforms are urgently needed.