Malawian President Joyce Banda on Tuesday said her country will take a long-dormant border dispute with Tanzania to the International Court of Justice for arbitration.
"The issue has gone too far and Malawi will seek international help to ensure that justice prevails," Banda told a news conference.
Malawi and Tanzania have been bickering over a largely undeveloped swathe of Lake Malawi, where Lilongwe has awarded a licence to British firm Surestream to explore for oil in northeastern waters near Tanzania.
"I have decided to take to the International Court of Justice to determine and resolve this wrangle," Banda said.
She said her country had cancelled a fresh round of talks in Tanzania last month after Lilongwe discovered that Tanzania has produced a new map.
"We decided to call off the follow-up dialogue meeting over the lake issue after we discovered that Tanzania had issued a new map with part of our lake."
Last month's talks hosted by Malawi ended in a dead-lock after the two neighboring states said they had failed to reach a common ground and differences still remained.
She said tensions were rising with reports that Malawi fishermen were being "abused and harassed."
"It is serious now. We have been informed by Tanzania that our boats should stop sailing on the lake otherwise they will blaze them up," said Banda.
Malawi claims ownership of the entire lake under a 1890 accord whose validity is disputed by Tanzania and wants a halt to the oil exploration currently under way to pave way for a diplomatic resolution.