Ecuador's foreign minister Ricardo Patino said they will release information on who planted the bug inside their embassy in London.
Patino said the device was used to collect "all kinds" of information from the office and was discovered before his visit to Assange, who has been staying in the embassy for more than a year. In a press conference in Quito, he said:
"We found that the device was used to collect all kinds of information in our embassy office. I didn't make it public at that time for we didn't want to affect the visit.
But we immediately conducted an investigation to find the source and I will release our result at tomorrow's press conference including the source of the device, who was using it and which department installed it."
Ricardo added that he hopes relevant countries or organizations could offer a reasonable explanation for the hidden listening device.
A hidden microphone has been found in the Ecuadorian Embassy in London, the country's foreign minister said.
It was found in the office of the ambassador Ana Alban during a routine search ahead of his visit to London on June 16, AFP reported.
Ricardo Patino, the Ecuadorian foreign minister, said: "We are sorry to inform you that we have found a hidden microphone in our embassy in London."
WikiLeaks founder Julian Assange has revealed he will not leave the Ecuadorian embassy in London even if sex charges against him are dropped, because he fears moves are already under way to extradite him to the US.
The disclosure was made on the first anniversary of his arrival at the embassy in a bid to avoid being sent to the US to be quizzed about the leaking of sensitive information to his whistle-blowing website.
He said: "The strong view of my US lawyer is that there is already a sealed indictment which means I would be arrested, unless the British government gave information or guarantees that would grant me safe passage.
"We know there is an ongoing investigation in the US and we know I am a target of the Federal grand jury. There is a 99.97% chance that I will be indicted.
"So if the Swedish government drops their request (to go to Sweden) tomorrow, I still cannot leave the embassy.
"My lawyers have advised me I should not leave the embassy because of the risk of arrest and extradition to the US."
A working group of legal experts is to be set up by the UK and Ecuadorian governments to try to break the deadlock over the future of WikiLeaks founder Julian Assange.
Mr Assange has been inside Ecuador's London embassy for almost a year, fearing he will be extradited to the United States if he travels to Sweden to answer allegations of sexual assault against two women.
Ecuador's foreign minister Ricardo Patino said it was "grossly unjust" that Mr Assange could not leave the embassy without being arrested.
Julian Assange is prepared to remain in the Ecuadorian Embassy for five years, said Ecuador's foreign minister Ricardo Patino.
The Foreign Office said William Hague met his Ecuadorian counterpart to discuss the case of WikiLeaks founder Julian Assange, who has been granted political asylum inside the Ecuadorian embassy, but that no "breakthrough" had been made.
A statement said:
Foreign Secretary [William Hague] and Foreign Minister Patiño agreed to keep channels of communication open, but made no breakthrough on Julian Assange.
The two ministers held a bilateral meeting this morning for 45 minutes.
Ministers agreed that officials should establish a working group to find a diplomatic solution to the issue of Julian Assange, but no substantive progress was made.
The Foreign Secretary was clear once again that any resolution would need to be within the laws of the United Kingdom.
Assange is wanted for questioning over two sexual assault allegations in Sweden and will be arrested if he leaves the embassy building.
Ecuador's foreign minister will meet Foreign Secretary William Hague today to discuss the future of WikiLeaks founder Julian Assange.
Ricardo Patino said Mr Assange was in "good spirits" despite the "limitations" of his accommodation inside the Ecuadorian embassy in London, where he has been since June 19 last year.
The WikiLeaks founder is wanted for questioning in Sweden over sex allegations by two women - which he denies - but fears being extradited to the United States if he goes to Sweden.
Ecuador's foreign minister tonight met with WikiLeaks founder Julian Assange inside the embassy where the Australian has been staying for the past year.
Ricardo Patino said Mr Assange was in "good spirits" despite the "limitations" of his accommodation inside the Ecuadorian embassy in London.
Mr Patino added that the Ecuadorean government remains "firmly committed to protecting his human rights" and that it is seeking "cast iron assurances to avoid any onward extradition".
Mr Assange has been living inside the embassy since 19 June last year. He is wanted for questioning in Sweden over sex allegations by two women - which he denies - but fears being extradited to the United States if he leaves.
A senior Ecuadorian minister will make a brief visit to the UK ahead of talks over the future of WikiLeaks founder Julian Assange.
Ecuador's foreign minister, Ricardo Patino, is due to meet Mr Assange at the country's embassy later today, before holding talks with Foreign Secretary William Hague tomorrow.
The Australian has been inside the embassy since June 19 last year and has since been granted political asylum.