Former friends and foes alike from across the world paid tribute Monday to the late British prime minister Margaret Thatcher, remembering an "extraordinary leader" who stamped her authority everywhere.

The "Iron Lady" was a polarising figure in Britain and beyond during her time in office, but foreign leaders Monday were unanimous in acknowledging her place in 20th century history, with Barack Obama mourning a "true friend of America".

German Chancellor Angela Merkel hailed Thatcher as "an extraordinary leader in the global politics of her time".

Former Soviet leader Mikhail Gorbachev, who held frequent meetings with Thatcher in the 1980s as the Cold War drew to a close, said that Thatcher will go down in history.

"Margaret Thatcher was a great politician and a bright individual. She will do down in our memory and in history," the Nobel Peace Prize winner said in a statement released by his foundation.

"Thatcher was a politician whose words carried great weight," he added, calling her death "sad news".

Thatcher, who once famously said of Gorbachev that "this is a man I can do business with," died of stroke on Monday at the age of 87.

Gorbachev admitted that their first meetings were tense because the Soviet Union was still a few years from falling apart, and his own commitment to the Communist Party made their relations sometimes rocky.

But he said that the two leaders always treated each other with the utmost respect, listening to what the other had to say closely.

"Our first meeting in 1984 gave the start to relations that were at times difficult, not always smooth, but which were serious and responsible for us both," he noted.

Fellow Cold War hero Lech Walesa, the Polish dockyard worker whose pro-democracy Solidarity movement helped create the first cracks in the Soviet system in the 1980s, said Thatcher helped Communism fall in his own country.

"She was a great personality who has done many things for the world that contributed to the fall of Communism in Poland and Eastern Europe," Walesa told AFP.

But even those with reason to remember a sometimes divisive figure less fondly were quick to pay tribute to her huge personality.

In South Africa, a spokesman for the ruling African National Congress (ANC) recalled the differences between Thatcher and those fighting against Apartheid in the 1980s.

"She failed to acknowledge the ANC as the rightful party of governance, but was out of touch with the British people on that issue. It's water under the bridge," said spokesman Keith Khoza.

But he added: "Margaret Thatcher was a leader of note, despite disagreements in policy between her and the ANC."

In Brussels, European Commission head Jose Manuel Barroso paid tribute to Thatcher's "contributions" to the growth of the European Union, despite her reservations about continental European integration.

Expressing his "deepest regrets" to the UK government, Barroso said she had been "a circumspect yet engaged player in the European Union" who "will be remembered for both her contributions to and her reserves about our common project."

Outside Europe, Israel's conservative Prime Minister Benjamin Netanyahu was one of the first world leaders to speak publicly of Thatcher's passing, saying that "she was truly a great leader".

In Spain, Prime Minister Mariano Rajoy said Thatcher's "firm determination to make reforms" was an inspiration to European leaders who are currently "facing very complex challenges that require great efforts and political courage."

French President Francois Hollande on Monday hailed former British prime minister Margaret Thatcher as a "great figure who left a profound mark on the history of her country."

"Throughout her public life, with conservative beliefs she fully assumed, she was concerned with the United Kingdom's influence and the defence of its interests," Hollande said.