UN chief Ban Ki-moon on Friday told Syria's prime minister in Tehran that fighting must stop in Syria "with the primary responsibility resting on the government to halt its use of heavy weapons", AFP reported.
In the meeting with Syrian Prime Minister Wael al-Halaqi and Foreign Minister Walid Muallem, Ban said he set out "my demands for all sides to cease all forms of violence," with Damascus bearing the greatest responsibility.
"What is important at this time is that all the parties must stop the violence. All those actors who may be providing arms to both sides... must stop," Ban said at a news conference broadcast live on Iranian television.
The UN secretary general held his meeting with Halaqi on the sidelines of a two-day Non-Aligned Movement summit in Tehran that was to end on Friday.
Ban said he had asked Iran to support his call on Syria, "and I have a strong assurance from Iran that it will do so."
He also said he had a series of meetings with joint UN-Arab League envoy Lakhdar Brahimi, who has taken over from Kofi Annan international efforts to broker peace in Syria.
has claimed more than 26,000 lives since it began in March 2011, according to the Syrian Observatory for Human Rights.
Iran, the principal ally of the regime of Syrian President Bashar al-Assad, has accused the United States, Saudi Arabia, Qatar and Turkey .
The Syrian opposition and US officials in turn allege that Iran is giving military help to Assad.
Earlier on Friday, Halaqi met Iran's supreme leader Ayatollah Ali Khamenei, who said the United States and Israel were responsible for the Syrian conflict, saying they were "flooding weapons" to rebels there.
"The main and behind-the-scenes operators behind the painful issues in Syria are America and the Zionist regime," Khamenei said, according to his official website.
Khamenei called the bloodshed in Syria "unacceptable," but said it was "the Syrian government that has been the victim of current events."
He urged Halaqi to "remove all pretexts" preventing the opposition from engaging in dialogue and to press on with promised political reforms.
Halaqi thanked Khamenei for Iran's support, and delivered greetings from Assad, who did not attend the NAM summit.
"The Syrian government is determined to confront all terrorist groups and to cleanse areas of these groups while moving ahead with political reforms and national dialogue," Halaqi was quoted as saying.