The UN Security Council, European Union and the US appealed for an end to the protests that have engulfed about 20 countries, the most violent in the Middle East.
Six people were killed and dozens injured in Friday's violence alone.
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Two protesters were killed in Sudan on Friday as thousands of people demonstrated against a US-made film mocking Islam, attacking the embassies of Britain, Germany and the United States.
Security forces used tear gas against around 5,000 demonstrators who stormed the embassies, setting the German mission ablaze, an AFP reporter said.
Protests over the film first broke out on Tuesday in Egypt and Libya, where the US consulate in Benghazi came under attack by an armed mob which killed the US ambassador and three other Americans.
"The members of the Security Council expressed their deep concern at these attacks, recalling that the very nature of diplomatic premises is peaceful and that diplomats have among their core functions the promotion of better understanding across countries and cultures," said the statement read by German Ambassador Peter Wittig, who holds the council's rotating presidency.
The council issued a reminder of "the fundamental principle of the inviolability of diplomatic and consular premises," condemning violence against the sites as "unjustifiable regardless of their motivations."
The council statement was made one day after UN Secretary-General Ban Ki-moon condemned the "hateful" anti-Islam Internet film that he said was deliberately intended to incite bigotry.
A Coptic Christian living in California is apparently behind the film, which the US government has strongly condemned.
EU foreign policy chief Catherine Ashton issued an appeal for "peace and retraint" after angry mobs attacked the embassies of EU members Britain and Germany in Khartoum. US diplomatic missions have also been attacked in several Arab countries.
"I condemn in the strongest terms the attacks against diplomatic missions in several countries," Ashton said in a statement.
European Commission President Jose Manuel Barroso earlier condemned the attacks on the British and German embassies in Khartoum as unacceptable and against "the rules of the civilised world."
"Nothing justifies these kinds of attacks," Barroso said, noting that at a meeting with Egyptian President Mohamed Morsi Thursday, he had equally condemned the attacks on Islam which have sparked widespread protests in the Muslim world.
US President Barack Obama vowed to 'stand fast' against spreading anti-US violence raging in the Arab world, as he mourned four Americans slain in Libya after their remains were flown home.
He said that the "awful" loss of lives during the protests and terrible images may cause some to question the dangerous work of US diplomats abroad, but argued that America must not abandon its global mission to spread dignity and freedom.
"Even as voices of suspicion and mistrust seek to divide countries and cultures from one another, the United States of America will never retreat from the world," he vowed.
