Britain said it was "determined" to extradite Julian Assange to Sweden to face sexual assault claims as Ecuador said it would reveal its decision over the WikiLeaks founder's asylum claim on Thursday.
"The UK has a legal obligation to extradite Mr. Assange to Sweden to face questioning over allegations of sexual offences and we remain determined to fulfil this obligation," said a Foreign Office spokesman.
Mr. Assange, a 41-year-old Australian national, took refuge at the Ecuadorian embassy in London on June 19 to avoid extradition to Sweden, which he says plans to surrender him to US authorities.
Ecuador's Foreign Minister Ricardo Patino slammed the British government during a press conference on Wednesday, revealing he had received a letter claiming police had the legal right to enter the embassy and arrest Mr. Assange.
"They could storm our embassy if Ecuador does not hand over Julian Assange," Mr. Patino said.
"The position taken by the government of Great Britain is unacceptable, both from the political and the legal point of view," the foreign minister said.
He warned that entering the embassy without authorization "would be a flagrant violation of the Vienna Convention" on diplomatic relations.
Britain's Foreign Office later released a statement saying it hoped a "mutually acceptable" solution could still be found, but warned it would do all it could to extradite the former hacker.
"We have an obligation to extradite Mr. Assange and it is only right that we give Ecuador the full picture," the spokesman said of the letter.
"Throughout this process have we have drawn the Ecuadorians' attention to relevant provisions of our law, whether, for example, the extensive human rights safeguards in our extradition procedures, or to the legal status of diplomatic premises in the UK.
The law which Britain is threatening to invoke is the Diplomatic and Consular Premises Act 1987 which allows it to revoke the diplomatic immunity of an embassy on UK soil.
WikiLeaks spokesman Kristinn Hrafnsson told AFP that the threat to storm the embassy was "extremely serious" and said that the group's legal team refuted its legality.
The organisation's Twitter feed called on supporters to protest outside the embassy, which is situated in the upper-class neighbourhood of Kensington.
Around 10 police were present outside the embassy late Wednesday, according to an AFP reporter, while two were visible inside the lobby itself.
WikiLeaks spokeswoman Sarah Harrison was also seen entering the building, but refused to speak to reporters.
Mr. Patino said that Ecuador "has made a decision" and will announce it Thursday at 7:00 am. Mr. Patino had earlier presented a report on the case to Ecuadorian President Rafael Correa.
Quito had said it was reviewing the sexual misconduct allegations as it weighs his asylum request. Mr. Assange maintains he had consensual sex with the alleged Swedish victims.
Mr. Correa has said that the mere possibility that Mr. Assange could face capital punishment in the United States could be reason enough for his government to grant the activist's asylum petition.
Mr. Assange's WikiLeaks website infuriated Washington when it released hundreds of thousands of secret war reports from Iraq and Afghanistan and countless US embassy cables containing unguarded and at times embarrassing remarks by a number of world leaders and diplomats.