The Independent International Commission on Decommissioning told Reuters in a statement, "We have now reported to the British and Irish governments that we have observed and verified events to put beyond use very large quantities of arms which we believe are all the arms in the IRA's possession."
The IRA also issued a statement, saying, "The IRA leadership can now confirm that the process of putting arms beyond use has been completed."
The weapons, including ammunition, rifles, machine guns, mortars, missiles, handguns and explosives, were made "permanently inaccessible or permanently unusable," said John de Chastelain, a retired Canadian general who has led efforts to disarm the IRA since 1997, the Associated Press reported.
The amount of weapons was consistent with police and army estimates of the IRA's holdings, he said.
Mitchel McLaughlin, a senior official of Sinn Fein, the IRA's political ally, said he hoped disarmament would prove "a defining and, hopefully, a liberating moment for the process" that would promote "confidence and generosity in response from our opponents."
The largely Protestant, pro-British hardline Democratic Unioinist Party, however, dismissed the IRA's actions in advance.
"We have seen stunts, hype and spin time out of number ... so it's going to be a lot harder, more difficult, more challenging to get people to accept this as genuine," said Democratic Unionist Chairman Nigel Dodds, quoted the AP.
British officials are hopeful that the disarmament will help reinvigorate Northern Ireland's provincial legislature, which was established by the 1998 agreement to share power between Protestant and Roman Catholic parties. The governing body was suspended in 2002 after allegations of IRA spying and the threatened boycott of the larger pro-British parties.
Britain first demanded the IRA disarm in 1993 as they best way it could prove it had renounced violence.
The focus on weapons came about after the IRA purchased more than 130 tons of arms and explosives from Libyan dictator Moammar Gadhafi in the mid-1980s, reportedly enabling the organization to bomb London for decades if it so desired, according to the AP.