Human Rights Watch says the Syrian government is using Soviet-made cluster bombs.. JR NEWS.

Russia fights claim that Syria is using Russian-made cluster bombs.

STORY HIGHLIGHTS

• Human Rights Watch says the Syrian government is using Soviet-made cluster bombs
• Russia's foreign minister says there is no confirmation of the group's report
• Cluster bombs release dozens of smaller bombs, which can maim or kill long after impact
• Special envoy Brahimi was given a proposal by Iran to resolve the Syrian crisis

(CNN) -- The war in Syria has led to another war of words internationally, with Russia slamming a report that accuses the Syrian air force of using Russian-made cluster bombs.

"There is no confirmation to this. ... There are loads of weapons in this region, including in Syria and other countries of the region, and arms are supplied there in large quantities and illegally," Foreign Minister Sergey Lavrov said, according to Russia's RIA Novosti news agency.

Citing witnesses and videos, Human Rights Watch released a report Sunday saying Syrian government forces were using cluster bombs -- explosives that can kill or disfigure anyone who touches its fragments.

The report says the cluster bombs are Soviet-made, but says it's unclear how or when Syria allegedly acquired them.

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"Syria's disregard for its civilian population is all too evident in its air campaign, which now apparently includes dropping these deadly cluster bombs into populated areas," said Steve Goose, arms director at Human Rights Watch. "Cluster bombs have been comprehensively banned by most nations, and Syria should immediately stop all use of these indiscriminate weapons that continue to kill and maim for years."

More than 70 countries have signed a treaty banning the use of cluster bombs, but Syria is not among them.

The bombs are particularly vicious because they explode in the air, sending dozens or hundreds of smaller bombs over an area the size of a football field, according to Human Rights Watch.

"These bomblets often fail to explode on initial impact, leaving duds that act like landmines and explode when handled," the group said.

In other developments:

Diplomatic front: Special envoy to Syria visits Iran and Iraq

Desperate to find a solution to Syria's bloody civil war, international envoy Lakhdar Brahimi visited the country's key ally in the region, Iran, before heading to Iraq on Monday.

Brahimi met with Iranian President Mahmoud Ahmedinajad, calling for an end to the flow of arms to both sides of the conflict, Brahimi's spokesman said Monday.

Rebel fighters have accused Iran of sending advisers to help Syrian President Bashar al-Assad battle the popular uprising.

Before Brahimi left, Foreign Minister Ali Akbar Salehi handed him a "written and unofficial proposal" for resolving the Syrian crisis, Iran's IRNA news agency reported Monday. Details of the plan were not publicized.

Brahimi, the U.N.-Arab League envoy to Syria, is on a tour of key countries in the region. Over the weekend, he met with Syrian opposition leaders in Istanbul and with Turkish officials.

Turkey is becoming more intertwined with the Syrian crisis. The country is hosting about 100,000 Syrian refugees, and cross-border shelling that killed five Turkish civilians led to a heightened confrontation between the two neighbors.

Turkish Prime Minister Recep Tayyip Erdogan has repeatedly denounced al-Assad, accusing him of massacring his own people and calling for his resignation.

Syria has berated its former ally, accusing Turkey of arming and funding Syrian rebels. CNN journalists have witnessed light weapons -- assault rifles, rocket-propelled grenades and machine guns -- coming from Turkey to Syrian rebels.

Background

The opposition says more than 30,000 people have been killed since March 2011, when anti-government protesters took to the streets calling for political reform and an end to four decades of al-Assad family rule. The government responded with a violent clampdown, spawning an armed conflict that has spiraled into a civil war.

CNN cannot independently confirm reports of casualties in Syria because the government has restricted access to international journalists.

CNN's Samira Said, Holly Yan and Amir Ahmed contributed to this report.