Syrian Foreign Minister Walid al-Muallem (L), Russian Foreign Minister Sergey Lavrov (C) and Iranian Foreign Minister Mohammad Javad Zarif attend a joint press conference in Moscow, Russia, on April 14, 2017. (Xinhua/Evgeny Sinitsyn)

MOSCOW, April 14 (Xinhua) -- Russia, Iran and Syria proposed an on-site investigation into the use of chemical weapons in Syria last week, Russian Foreign Minister Sergei Lavrov said Friday.

"We insist on conducting a meticulous, objective and unbiased investigation into the alleged chemical weapon attack by Syrian aircraft on April 4," Lavrov said at a joint press conference after talks with his Iranian and Syrian counterparts, Mohammad Javad Zarif and Walid al-Muallem.

The three agreed that the probe should be carried out by a well-balanced team of experts under the auspices of the Organization for the Prohibition of Chemical Weapons (OPCW), the UN chemical weapons watchdog, Lavrov said.

Russia and Iran hailed the readiness of the Syrian government to accept such a mission, he added.

On April 7, the United States launched 59 cruise missiles against a Syrian military airfield in the province of Homs in response to the gassing of civilians in Khan Sheikhoun in the province of Idlib

Washington blamed the Syrian government for the attack. But Russia said it might have been caused by the explosion of chemical weapons stored by rebels in a local depot during a raid by the Syrian Air Force.

Russia, Iran and Syria unanimously regarded the U.S. missile strikes as an aggression in brutal violation of international law and the UN Charter, Lavrov noted.

"We insist that the United States and its allies should respect the sovereignty of Syria and abstain from similar actions," he said.

At the press conference, Syria's Muallem reiterated that his government no longer possesses chemical weapons and the destruction of its previous stockpiles had been confirmed by the OPCW.

"We do not use chemical weapons against terrorists or our own people. We condemn any use of chemical weapons," said the Syrian top diplomat.

For his part, Iran's Zarif said the gassing accusation should be clarified as soon as possible.