Ricardo Patino said Assange was in "good spirits" despite the "limitations" of his accommodation.
The foreign minister is in Britain for a meeting with counterpart William Hague to try and find a solution to the impasse which has led to Assange spending one year in the embassy in a bid to avoid extradition to Sweden.
The foreign minister arrived at the embassy at 6.30pm and waved to around one hundred Assange supporters before heading inside the building.
Shortly afterwards, the pair opened a window in Assange's ground floor residence and greeted supporters before returning inside for talks, which lasted around an hour.
"I have just finished meeting with Julian Assange who is in good spirits despite the limitations of his accommodation," said Patino.
"I was able to say face to face to him, for the first time, that the government of Ecuador remains firmly committed to protecting his human rights and that we continue to seek cast iron assurances to avoid any onward extradition to a third state."
Assange and WikiLeaks insist that Britain's real aim in seeking to deport him to Sweden, where prosecutors want to quiz him over allegations of rape and sexual assault, is to send him to the United States.
"During the meeting we were able to speak about the increasing threats against the freedom of people to communicate and to know the truth, threats which come from certain states that have put all of humanity under suspicion," added Patino.
Hague and Patino are searching for a diplomatic solution to the stalemate, which was triggered when Assange turned up at the embassy demanding asylum on June 19 last year.
Assange said Sunday's meeting was "very good" and that Patino had "set out how he and the Ecuadorian government are actively seeking a solution to my present situation.
"I remain immensely grateful to the support Ricardo, President (Rafael) Correa and the people of Ecuador have shown me over the last year," he added.
Crowds gathered outside the embassy carrying banners offering support to Bradley Manning, the US Army private who is facing charges that he passed hundreds of thousands of secret government files to WikiLeaks.
Others called for former US spy Edward Snowden, who recently exposed vast US surveillance programmes, to be protected.
Assange supporter Edwin Pazmino urged Britain to strive for an agreement at Monday's talks.
"Coming from a country which was a pioneer of human rights, never has there been such an injustice," said Pazmino, a 43-year-old Ecuadorian.
"I hope that tomorrow at the meeting with the British minister we will get something positive and Britain will give Assange safe passage to Ecuador," he added.