Lavrov made the statement at his annual news conference in Moscow, in response to a question about U.S. suspicions that a Russian ship had delivered arms to Syria.
"We do not think it is necessary to explain or justify ourselves because we are not violating any international agreements or UN Security Council resolutions," Lavrov said.
"We are only trading items with Syria that are not banned by international law."
A Russian-operated ship carrying what a Cypriot official said was bullets arrived in Syria last week from St. Petersburg after being held up in Cyprus.
Lavrov also said that Russia, together with China -- another veto-holding Security Council member -- would stand firm against foreign intervention.
Russia has been a strong supporter of Syrian President Bashar al-Assad during a 10-month government crackdown that the United Nations says has killed more than 5,000 civilians, refusing to join calls for him to step down.
Russia joined China in October to veto a Western-backed resolution against Assad's government.
Activists, meanwhile, said the Syrian Army struck a surprise cease-fire deal with rebels in the town of Zabadani near Damascus on January 18.
The truce was reportedly reached between town leaders and Deputy Defense Minister Assef Shawkat, Assad's brother-in-law.
compiled from agency reports