Sweden's international prosecutor will probe whether a Swedish oil company with connections to Foreign Minister Carl Bildt had any role in war crimes committed in Sudan.

• Swedish oil firm blamed for war crimes in Sudan

Magnus Elving "today decided to launch a preliminary investigation regarding crimes against humanitarian law in Sudan during the years 1997 to 2003," the prosecutor's office said in a statement.

Sweden's national police will assist with the probe into allegations made in a recent report -- "Unpaid Debt" -- by ECOS, an umbrella group of European organisations "working for peace and justice in Sudan."

The report, published this month, claimed Sweden's Lundin Petroleum, previously Lundin Oil, and its partners Petronas Carigali Overseas of Malaysia and OMV Exploration from Austria "may have been complicit in the commission of war crimes and crimes against humanity" in southern Sudan.

By launching oil exploration in such an unstable region, the consortium had set the wheels in motion for a power struggle that led to numerous crimes, including widespread "killing of civilians, rape of women, abduction of children, torture and forced displacements," the report claimed.

According to ECOS, some 12,000 people were killed or died from hunger, exhaustion and conflict-related diseases in the area during the seven years in question, while around 160,000 people were forcibly displaced.

While not mentioning Lundin by name, the Swedish prosecutor's office said "the aim of the preliminary investigation is to examine whether there are individuals with links to Sweden who can be suspected of involvement in crimes."

Although not mentioned in the prosecutor's statement, Bildt was expected to be drawn into the inquiry, since Sweden's top diplomat was on Lundin's board at the time.

Bildt, who resigned from Lundin's board in 2006, said at a press conference Monday he would not comment on the content of the preliminary investigation, pointing out that it is "very vague."

"I think it is important for everyone, not just myself, not to comment or politicise what the prosecution authorities are doing," he said, adding that before he commented "I'd like to know first what this is actually about and what it is not about."

"I don't even know if I am part of it," he insisted.

Bildt did however comment on the ECOS report, which he described as the work of a lobby that has long made similar allegations.

"They are pushing their agenda," he said, stressing that in his opinion, Lundin's activities in Sudan had "actually played a small part in creating attention that in the end led to a peace process," with a peace agreement signed in 2005.

"The international presence had, I think, a positive impact," he said.

The Swedish foreign minister thus echoed claims reiterated by the company's current board that it had if anything "contributed to peace and development in Sudan."

Several high-ranking members of Sweden's left-leaning opposition meanwhile reacted strongly to the news of the prosecutor's probe, with a member of the formerly communist Left Party going so far as to call for Bildt to resign.

And Thomas Bodstroem, a member of parliament with the main opposition Social Democrats and a former justice minister, called for Bildt to take a "time-out" from politics, although he stopped short of asking him to step down.

"Never before in contemporary Swedish history has a criminal investigation meant that such a high-ranking politician could become the focus of charges for such a serious crime," he charged on his blog.

Bildt took the criticism in stride, pointing out that "there is obviously campaigning going on" ahead of Sweden's September 19 elections.

"I'd like to ask the gentlemen to calm down a little and wait to see what this (investigation) is actually about," he said.

Swedish Prime Minister Fredrik Reinfeldt also told the TT news agency Monday it was too early to draw any conclusions about the case.

"It is always important to let the judicial system work through things so we know (which direction an investigation is heading) before we comment," he said.