Computer hacking collective Anonymous claims it has attacked a number of Government websites in protest over the Julian Assange case.
Websites including that of the Home Office and the Ministry of Justice were affected by the group, which has been using the hashtag "OpFreeAssange" on Twitter.
WikiLeaks founder Mr Assange, who is wanted in Sweden for questioning on sexual assault allegations, has been seeking refuge in the Ecuadorian embassy in London for two months with the British authorities threatening to arrest him if he steps outside.
A Ministry of Justice spokeswoman said: "The Ministry of Justice website was the subject of an online attack last night at around 2000 hours.
"This is a public information website and no sensitive data is held on it. No other Ministry of Justice systems have been affected.
"Measures put in place to keep the website running mean that some visitors may be unable to access the site intermittently.
"We will continue to monitor the situation and will take measures accordingly."
A spokeswoman for the Home Office denied its website was "hacked", but added: "It was targeted by protesters on Monday night but only experienced very minor interruption to the service.
"We had measures in place to protect the site and no other Home Office systems were affected."
It is the latest development in the diplomatic row between the South American country and the UK.
Last night Ecuador's president Rafael Correa said it would be "suicide for Great Britain" if authorities tried to enter his country's embassy to reach Mr Assange.
Speaking on state television, Mr Correa said such a course of action would be "suicide for Great Britain because then people could enter their diplomatic premises all around the world and they wouldn't be able to say a thing".
He added: "While the United Kingdom hasn't retracted nor apologised, the danger still exists.
"Remember that David beat Goliath. And with many Davids it's easier to bring down a number of Goliaths.
"So we're hoping for clear and coherent backing because this violates all inter-American law, all international law, the Vienna Convention and all diplomatic traditions of the last, at least, 300 years on a global scale."
Foreign ministers from across South America have called for dialogue between the two countries, issuing a statement of support for Ecuador following the meeting of the Union of South American Nations (Unasur) in the country.
In the statement, released after the 20-minute meeting, the ministers "condemned the threat of the use of force between states" and reiterated "the right of states to concede asylum".
Unasur's meeting was held a day after Cuba, Venezuela, Bolivia, Nicaragua and Argentina endorsed Ecuador's asylum decision.
Brazil, Colombia, Mexico and Chile are among Latin American nations that have not taken a stand.
On Sunday, Mr Assange made his first public appearance since he entered the building, calling on Washington to "renounce its witch-hunt" against WikiLeaks.
The Australian thanked Ecuador for taking a "stand for justice" in giving him political asylum when he spoke from the embassy's balcony.
Foreign Secretary William Hague has made it clear Mr Assange will not be allowed safe passage out of the UK.
Mr Assange denies the allegations and fears being transferred to America if he travels to contest them.
He enraged the US government in 2010 when WikiLeaks published tranches of secret US diplomatic cables.
During his speech, Mr Assange thanked Ecuador and other helpful South American nations and supporters around the world.
He said: "On Wednesday night, after a threat was sent to this embassy, the police descended on this building. You came out in the middle of the night to watch over it, and you brought the world's eyes with you.
"Inside this embassy in the dark, I could hear teams of police swarming up inside the building through its internal fire escape.
"But I knew there would be witnesses, and that is because of you.
"If the UK did not throw away the Vienna Convention the other night, it is because the world was watching. And the world was watching because you were watching."
Ecuador has said it granted asylum because neither Britain nor Sweden would offer guarantees that they would not allow Mr Assange's extradition to the United States. Supporters of Mr Assange say they fear he has been secretly indicted by a grand jury in the US.
Mr Correa has said there is sufficient reason to fear Mr Assange, who published the largest trove of US secrets ever in 2010, would be denied due process in the United States and could face life in prison or even the death penalty.