Russia has been one of Syria's strongest allies and, along with China, has vetoed three Western-backed resolutions proposed to the United Nations that aimed to pressure Assad to end the violence.
Lavrov, speaking after his talks with U.N. Secretary-General Ban Ki-moon in the Black Sea resort of Sochi, avoided specific comment on the Yakhont or other weapons deals, but insisted that the deliveries don't violate any international treaties.
Asked about Western criticism of Russia over its missiles sales to Syria, Lavrov said: "I don't understand why the media are trying to make a sensation out of it. We haven't tried to conceal that we have been supplying weapons to Syria under contracts signed earlier without violating any international treaties and Russian laws."
He insisted that Russia is providing Syria "primarily with defensive weapons, air defense systems." Lavrov said that such weapons shipments don't tilt the balance of power in the region and can't be used by the Syrian regime to fight the rebels in the country's civil war.
In Washington, State Department spokeswoman Jennifer Psaki told reporters that "it seems that these cases that were reported this morning have been previously reported." She added that "we're not aware of new shipments of these specific missiles."
Also Friday, a squadron of five Russian navy ships from the Pacific Fleet arrived in the port city of Limassol in the Mediterranean island of Cyprus, a Russian navy statement said. The Admiral Panteleyev destroyer, two amphibious landing vessels, a tanker and a tugboat have replaced a previous group of Russian navy ships that have sailed back home.
Russia has pledged to revive a permanent presence in the Mediterranean its navy had during Soviet times. Rotating squadrons of Russian navy ships have visited the area repeatedly over the past two years in what was seen as a demonstration of their military's global reach and a gesture of support for Syrian President Bashar Assad's regime.
Some observers said Moscow could use the amphibious landing ships included in most squadrons to evacuate equipment and military personnel from the Russian base in the Syrian port of Tartus, the only such outpost Russia has outside the Soviet Union.
Military experts say the deployments stretch the capability of the Russian navy, which has only started to recover from its post-Soviet decline and has only a few ships capable of taking part in such missions.
Human Rights Watch said its researchers found physical evidence that Syrians were tortured, including with a device which former detainees said was used to stretch or bend victims' arms and legs. The group also found documents indicating Raqqa residents were detained for legal actions like demonstrating or helping the injured.
Rights groups and opposition activists have long claimed that civilians have been detained arbitrarily, tortured, and sometimes have disappeared since the uprising against Assad's regime began. HRW's findings appear to be one of the largest discoveries of physical evidence bolstering those claims to date.
"The documents, prison cells, interrogation rooms, and torture devices we saw in the government's security facilities are consistent with the torture former detainees have described to us," said Nadim Houry, deputy Middle East director for HRW.
HRW has been documenting abuses on both sides of Syria's civil war during the 26 months of conflict.
The group says abuses by the Assad regime remain far more deadly, systematic and widespread, including attacks on civilians with indiscriminate battlefield weapons such as widely banned cluster bombs. But the rights group also says rebel abuses have increased in frequency and scale in recent months.
In Raqqa, the group's researchers inspected the State Security and Military Intelligence branches and three other detention centers formerly managed by Criminal Security, Political Security, and Air Force Intelligence. Government forces abandoned all these institutions, which are now controlled by the rebels, the group said.
Four former detainees said that officers and guards tortured them, HRW said.
In one method of torture the HRW report details, the victim is tied to a flat board, sometimes in the shape of a cross. In some cases guards stretched or pulled their limbs or folded the board in half so that their face touched their legs, causing pain.
Syria's conflict started as a peaceful uprising in March 2011. It became an armed conflict when opposition supporters took up arms to fight a brutal government crackdown on dissent.
At least 70,000 people have been killed and millions forced out of their homes. In Geneva, the U.N. refugee agency said the number of Syrian refugees has surpassed the 1.5 million mark.
Over the past year Syria has gradually descended into lawlessness, with a spike of kidnappings in largely rebel-controlled northern Syria as well as the government-held capital. Residents blame criminal groups that have ties to both the regime and the opposition for the abductions of wealthy residents traveling to Syria from neighboring Turkey and Lebanon.
On Friday, the Syrian Observatory for Human Rights expressed "grave concern" for two bishops who were abducted last month and have not been heard of since.
Gunmen pulled Bishop Boulos Yazigi of the Greek Orthodox Church and Bishop John Ibrahim of the Assyrian Orthodox Church from their car and killed their driver on April 22 while they were traveling outside the northern city of Aleppo. It was not clear who abducted the priests. No group has publically claimed it is holding the clerics.
According to the Britain-based activist group, the two were picked up at a checkpoint in Kfar Dael by Arabic-speaking foreign fighters believed to be from Chechnya.
In a statement, the Observatory called on both sides in the civil war to secure their release.
The group also said a suicide attacker blew up his car at an army checkpoint near the town of Tiba al-Imam in the central province of Hama, killing at least five soldiers. State news agency SANA said the bomber drove a tanker truck and that the attack killed two civilians and wounded four.
The Observatory and state media also reported clashes in the southern province of Daraa, where the uprising began, mostly in the town of Hirak. Syrian state TV said that among the rebels killed was a Jordanian citizen, known by the nom de guerre of Abu Zubair. It said he was a local commander of Jabhat al-Nusra, which is designated a terrorist group by the United States.
Associated Press writers Vladimir Isachenkov in Moscow and Matthew Lee in Washington contributed to this report.
U.N. says Syrian refugees top 1.5 million
The U.N. refugee agency says the number of Syrian refugees has surpassed the 1.5 million mark.
Agency spokesman Dan McNorton says that since this figure reflects only those who have registered with authorities, it "sadly means the actual number is much higher."
He told reporters Friday that the agency has registered close to 1 million refugees just since the start of this year from a country that had a population of 23 million but many more Syrians have not registered due to safety and other concerns
He says that conditions have deteriorated rapidly in Syria during the past four months when compared to the previous 20 months of the conflict.
Most of the Syrians are fleeing to Jordan or Lebanon, each of which has more than 470,000 registered refugees.