Russia used its veto power for the 12th time this week at the UN Security Council to block action directed at its Syrian ally.

The latest veto prevented the adoption of US-drafted resolution to investigate chemical weapons use in Syria aimed at identifying the perpetrators.

Britain, China, France, Russia and the United States are permanent Security Council members with veto powers. The other ten members are elected for two-year terms on a rotating basis.

UN resolutions require nine positive votes and no veto to be adopted.

Here's a look at Russia's 12 vetoes on Syria:

Chemical weapons

In all, Russia used its veto four times to block draft resolutions seeking to establish investigations of chemical weapons use in Syria's seven-year war.

A fifth veto was used to prevent a Western attempt to impose sanctions over chemical weapons use.

April 2018: Russia vetoed a US-drafted resolution after 12 countries backed the measure. China abstained, while Bolivia voted against.

October/November 2017: In less than a month, Russia used its veto three times to block draft resolutions on renewing a UN-led probe of chemical weapons attacks in Syria.

The Joint Investigative Mechanism (JIM) died on 17 November after several attempts by the Security Council to save the panel failed to meet Russian demands.

April 2017: Russia vetoed a draft resolution demanding that President Bashar al-Assad's government cooperate with an investigation into the deadly suspected chemical attack in the rebel-held town of Khan Sheikhun in April. China abstained.

February 2017: Russia and China again vetoed a UN resolution, drafted by Britain, France and the United States that would have imposed sanctions on Syria over chemical weapons use in the conflict.

Aleppo truce

December 2016: A resolution that calls for a truce in Aleppo is vetoed by both China and Russia. Egypt, New Zealand and Spain presented the measure.

The vote was 11 to 3 with one abstention from Angola. Venezuela voted against, alongside China and Russia.

October 2016: Russia alone vetoes a text proposed by France and Spain to halt the bombing of Aleppo, after presenting a rival draft that urged a ceasefire but made no mention of barring military flights over the city.

China abstained in that vote, the first time it did not veto a Syria draft resolution alongside Russia.

War crimes

May 2014: China and Russia block a French-drafted proposal for the Security Council to refer Syrian crimes to the International Criminal Court (ICC) is blocked. All 13 other council members backed the measure.

Russia accused Britain, France and the United States of hypocrisy in not wanting war crimes in Iraq referred to the ICC.

Sanctions threat

July 2012: China and Russia again veto a Western-backed resolution that threatens Syria with sanctions if it does not stop using heavy weapons.

Condemning Syria

February 2012: Russia and China again vetoed a draft resolution that condemns a Syrian government crackdown on the opposition, while the Security Council's other members voted in favour.

The veto sparked an international outcry, especially because it came a few hours after Syrian forces bomb the protest city of Homs, killing hundreds of people.

October 2011: Six months after the Syrian conflict began, Russia and China blocked a proposed UN resolution condemning grave human rights violations in Syria and threatening measures against President Bashar al-Assad's government.