Mikhail Gorbachev, 82, with whom the former British prime minister worked closely at the end of the Cold War, was expected to be one of a number of global figures attending.
Downing Street said consultation over the funeral guest list was continuing.
It has confirmed that Argentine President Cristina Fernandez de Kirchner will not be invited.
Queen Elizabeth II and Prince Philip are already confirmed for next Wednesday’s ceremony at St Paul’s Cathedral, London.
During her time in power Margaret Thatcher struck up an unlikely alliance with Mikhail Gorbachev, the reforming Soviet president who oversaw the end of the Soviet Union in 1991.
Following her death on Monday, Mikhail Gorbachev paid tribute to Baroness Thatcher as a “heavyweight politician and a striking person”.
On Wednesday, British MPs were recalled from their Easter break for a seven-hour Commons debate about Lady Thatcher.
British PM David Cameron said Margaret Thatcher “overcame the great challenges of her age”. Labour’s Ed Miliband paid tribute but said he disagreed “with much of what she did”.
Conservative MPs queued up in the Commons to pay their respects to Margaret Thatcher, who was prime minister from 1979 to 1990, but about half of Labour’s 256 MPs stayed away.
The Lords also held a debate on the former prime minister, with her former Cabinet ministers Lord Fowler and Lord Tebbit among those paying tribute.
The Guardian has reported that Commons Speaker John Bercow was taken aback by David Cameron’s request to recall Parliament because he thought tributes could be paid on Monday, when MPs were due to return.
The paper reports that a lengthy wrangle ensued, with David Cameron enlisting the support of Ed Miliband to overcome opposition to the move.
Responding to the report, a Downing Street spokesman said: “Only government ministers can request the recall of the House, which the Speaker then decides on.
“The prime minister felt given the strength of feeling following Lady Thatcher’s death it was appropriate to give the House an early opportunity to pay its respects.”
Discussions between PM David Cameron and the Speaker are ongoing about whether Prime Minister’s Questions, usually held at midday, will be cancelled next Wednesday to allow MPs to attend the funeral.
Speaker John Bercow could require MPs to attend the session later in the afternoon, rather than cancel it.
Meanwhile, the Foreign Office has said “an administrative error” led to inaccurate guidance being issued to diplomatic staff in embassies around the world after it was reported they had been told to wear mourning clothes on the day of the funeral.
They were later told it was unnecessary.
Guests who have said they will be attending Margaret Thatcher’s funeral include ex-Labour PM’s Tony Blair and Gordon Brown, as well as FW de Klerk, the last president of apartheid South Africa.
The Queen has not attended the funeral of a British politician since that of Sir Winston Churchill in 1965.
More than 700 armed forces personnel will line the route of the procession from Westminster to St Paul’s, including three bands whose drums will be covered in black cloth.
A gun salute will be fired from the Tower of London and the coffin will be carried into St Paul’s by service personnel from regiments and ships closely associated with the Falklands campaign.
The Metropolitan Police said it was working to ensure the day passed off safely, amid concerns that some people may use it as an opportunity to protest.
On the day of Margaret Thatcher’s death, there were small gatherings in various parts of the UK, notably in Glasgow, Bristol and London, with those taking part saying they were celebrating her death.
Met Commander Christine Jones urged anyone wishing to demonstrate to at the funeral to talk to the police.
“The right to protest is one that must be upheld,” she said.
“However, we will work to do that whilst balancing the rights of those who wish to pay their respects and those who wish to travel about London as usual.”
Margaret Thatcher’s family is meeting an unspecified amount of the expense of the funeral, thought to cover transport, flowers and the cremation, with the government funding the rest, including security.
Downing Street said the cost of the funeral would not be released until after the event.
Margaret Thatcher, who won three successive general elections, died “peacefully” on Monday after suffering a stroke while staying at the Ritz hotel in central London.
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