UNITED NATIONS, April 12 (Reuters) - Russia blocked a Western effort at the U.N. Security Council on Wednesday to condemn last week’s deadly gas attack in Syria and push Moscow’s ally President Bashar al-Assad to cooperate with international inquiries into the incident.

It was the eighth time during Syria’s six-year-old civil war that Moscow has used its veto power on the Security Council to shield Assad’s government.

In the latest veto, Russia blocked a draft resolution backed by the United States, France and Britain to denounce the attack in the town of Khan Sheikhoun and tell Assad’s government to provide access for investigators and information such as flight plans.

The toxic gas attack on April 4 prompted the United States to launch missile strikes on a Syrian air base and widened a rift between the United States and Russia.

Russian President Vladimir Putin said on Wednesday that trust had eroded between the two countries under U.S. President Donald Trump.

U.S. Secretary of State Rex Tillerson echoed that comment after meetings with Russian leaders in Moscow, saying that relations are at a low point with a low level of trust. Tillerson called for Assad to eventually relinquish power.

China, which has vetoed six resolutions on Syria since the civil war began, abstained from Wednesday’s U.N. vote, along with Ethiopia and Kazakhstan. Ten countries voted in favor of the text, while Bolivia joined Russia in voting no.

U.S. Ambassador to the United Nations, Nikki Haley, warned Moscow against protecting Assad, who relies on support from Russia and Iran in his conflict with mostly Sunni Muslim rebels.

“To my colleagues from Russia - you are isolating yourselves from the international community every time one of Assad’s planes drop another barrel bomb on civilians and every time Assad tries to starve another community to death,” Haley said during a Security Council meeting earlier on Wednesday.

Haley added: “Iran is dumping fuel on the flames of this war in Syria so it can expand its own reach.”

ATTACK INVESTIGATION

A fact-finding mission from the Organisation for the Prohibition of Chemical Weapons (OPCW) is investigating last week’s attack in a rebel-held area of northern Syria.

If it determines that chemical weapons were used, then a joint U.N./OPCW investigation will look at the incident to determine who is to blame. This team has already found Syrian government forces were responsible for three chlorine gas attacks in 2014 and 2015 and that Islamic State militants used mustard gas.

Britain’s U.N. Ambassador Matthew Rycroft told the Security Council that samples taken from the site of the April 4 attack had been analyzed by British scientists and tested positive for the nerve gas sarin. He said Assad’s government was responsible.

During a heated Security Council exchange before Wednesday’s vote, Russia’s deputy U.N. envoy Vladimir Safronkov told the 15-member body that Western countries were wrong to blame Assad for the gas attack.

“I’m amazed that this was the conclusion. No one has yet visited the site of the crime. How do you know that?” he said.

Syria’s government has denied responsibility for the attack.

Diplomats said that Russia has put forward a rival draft resolution that expresses concern at last week’s gas attack and condemns the U.S. strike on Syria. It was unclear if Moscow planned to put the text to a vote.

Syrian U.N. Ambassador Bashar Ja’afari said Syria had sent dozens of letters to the Security Council, some detailing “the smuggling of sarin from Libya through Turkey on a civilian air plane by using a Syrian citizen.”

“Two liters of sarin were transported from Libya through Turkey to terrorist groups in Syria,” he said, adding that the government does “not have these weapons.”

Western powers say the April 4 gas attack was carried out from the air and that Syrian rebels do not have any aircraft.

(Reporting by Michelle Nichols; Editing by Alistair Bell)