BEIJING - Three diplomats were injured in a mortar shell targeting the Russian embassy in Damascus on Sunday as Syria promptly handed over a preliminary report of its chemical weapons in fulfillment of its commitment made earlier.

In the mortar attack, one shell was fired by militants in the hotspot district of Brazeh onto the Russian embassy compound.

Brazeh has been a scene of fierce clashes raging on for days between the rebels and the Syrian government army.

"Three members of the embassy's staff received wounds not threatening their lives," the Russian foreign ministry said in a statement released in Moscow.

An investigation is underway and additional steps are being taken with the help of the Syrian side to tighten security of the Russian diplomatic mission, it noted.

The Russian embassy in Damascus has been targeted several times by the opposition militants who are trying to overthrow Assad's government.

Roughly one hour before the attack, Russian Foreign Minister Sergei Lavrov said in Moscow that his country was ready to send military observers to safeguard the experts and process of the destruction of Syria's chemical weapon stockpiles.

He said Russia doesn't intend to send a full military contingent, adding it has proposed an international presence on all spots where experts will work in Syria.

In The Hague, the Organization of Prohibition of Chemical Weapons (OPCW) said Syria handed over a preliminary report of its chemical weapons on Saturday.

The OPCW, a watchdog that polices the Chemical Weapon Convention banning the production, stockpiling and use of chemical weapons, has developed a global network with several prominent laboratories since its founding in 1997.

Syria is officially to become an OPCW member on Oct. 14. The organization, supervising the destruction of Assad's chemical arsenal, said the report has been reviewed by its verification teams, without giving further details.

Syria staved off a limited airstrike of the US by committing itself to disclosing and destroying its chemical weapons, with the help of an agreement brokered by the United States and Russia in Geneva last week, which sets a timetable for the Assad government to make public its chemical weapons arsenal by Saturday.

But US President Barack Obama, who blamed the Syrian government for using chemical weapons, said a military option is still on the table should Assad play stalling tactics.

In the latest interview with Fox News of the United States, Assad stressed commitment to the chemical weapon treaty, saying that it would cost 1 billion US dollars and take roughly one year to destroy his country's chemical weapon stockpiles.

Damascus has rejected Washington's accusation that the government troops gassed civilians with nerve agents during an attack on Aug. 21 near Damascus. Pointing finger at the rebels, the Syrian government said it has evidence that could incriminate them.

Meanwhile, five veto-wielding permanent members of the UN Security Council, deeply divided over Syria, are expected to churn out a resolution for the chemical weapon crisis this week.

Russian Foreign Minister Lavrov accused Sunday the United States of threatening to thwart the work on Syria by the OPCW if Moscow denies support to a UN resolution allowing the use of force.

He believed that the West wanted the resolution not only to support the OPCW decision on Syria, but also to carry provisions on the defense of human rights and the International Criminal Court.

"They see the Russian-US agreement as a chance for themselves to ... insist on a 'use of force' resolution targeting the (Assad) regime and defending the opposition," he said.

"It is an absolute deviation from what we have agreed on with (US Secretary of State) John Kerry -- to have an OPCW decision first and then to adopt a UN Security Council resolution supporting this decision but not based on Chapter VII," Lavrov said in an interview with Russia's Channel one television.