The assassination was condemned by world leaders.
Jack Lynch, the
taoiseach, said he was "horrified and saddened" by the killing, adding that the IRA "has brought death and sorrow to many thousands of innocent people and shame to all true Irish men and women". The
US Department of State said: "Americans will especially recall his great contribution to our common cause in World War II as well as his many services to this country and to the world since then."
Pope John Paul II was due to visit both Ireland and Northern Ireland, with a trip to Armagh, but the Northern Ireland part was cancelled following what
the Vatican described as "the brutal crimes" of the attacks on Mountbatten and the Warrenpoint ambush; the Pope described the assassination as "an insult to human dignity". Three days of state mourning were announced in Burma (now
Myanmar), while in India a week of mourning was observed. The British press condemned the attack, with the tabloid press expressing rage in their headlines, including the front page headlines in
The Daily Express ("These Evil Bastards") and
The Sun ("May the Bastards Rot in Hell"). ''
(The Republic'')—the republican newspaper published by
Sinn Féin, the political party associated with the IRA—carried a statement from the IRA in which they described the murders as "a discriminate act to bring to the attention of the English people the continuing occupation of our country". The statement continued: The British Army acknowledge that after ten years of war it cannot defeat us but yet the British government continue with the oppression of our people and the torture of our comrades in the
H-Blocks. Well, for this we will tear out their sentimental, imperialist heart. The Irish media was also condemnatory of the attack; in
The Irish Press,
Tim Pat Coogan wrote that the IRA's statement contained: Not a word of sympathy for the victims, two of them mere children, not a hint of regret, not a scintilla of compassion. Murder, whatever the supposed cause, never can be justified. But the murder of Lord Mountbatten – and that, it needs to be emphasised, is what it was – was particularly cruel. A friend of this country ... a friendly, genial man, popular with local people, blown to pieces while on one of his regular visits to this country. ... In their statement the Provisionals talk of his murder as "an execution". The execution of a 79-year-old man? Such hypocrisy will sicken and disgust all Irish people. Thatcher—prime minister of the newly elected government—hypothesised that the bombers had some links with Libya. Investigations by the security services showed no such connection, and that there was "no evidence that any member of this team has visited Libya". The
counter-terrorism consultant
Andy Oppenheimer states the IRA received £2 million from Syria, through a contact in the
Palestine Liberation Organisation, for the murder of Mountbatten and other acts. Others had different theories:
James Molyneaux—the leader of the
Ulster Unionist Party (UUP)—and
Enoch Powell—the UUP MP for
South Down—alleged involvement by the American
Central Intelligence Agency in Mountbatten's death, as part of a scheme to get Ireland to join
NATO, although this was deemed nothing more than a
conspiracy theory. The British government had pressed the government of Ireland over the cross-border aspect of IRA activity for some time; the death of Mountbatten in Ireland and the shooting at the survivors from south of the border at Warrenpoint, Britain argued, proved it. Thatcher asked Lynch to take action in the wake of the two attacks. The requested measures included closer cooperation between MI6 and the Irish Special Branch; that members of the
Royal Ulster Constabulary (RUC) could attend Garda interviews of suspects; and to allow British helicopters to fly up to into Irish airspace in pursuit of IRA units. Lynch
allowed overflights of up to ; when news of this became public, he was forced to resign. ==Investigation and trial==