Traces of sarin gas have been detected in blood and urine samples from victims wounded in the town of Khan Sheikhun in Syria, giving “concrete evidence” of its use in the attack, Turkey’s health minister has said.

Doctors and aid workers who had examined the wounded of last week’s massacre, which provoked the first US military strikes against the regime of Bashar al-Assad, said they exhibited symptoms of exposure to a nerve agent similar to sarin, as well as a second chemical that may have been chlorine.

But the tests in Turkey, where many of the victims were taken for treatment due to the lack of medical facilities inside Syria, offer the first insight into the actual toxins used in the attack that killed over 80 people and drew worldwide condemnation and a renewed focus on the brutal conduct of the war.

The Turkish health minister Recep Akdağ said isopropyl methylphosphonic acid, a chemical that sarin degrades into, was found in the blood and urine samples taken from the patients who arrived in Turkey. Some 30 victims were brought across the border following the attack last Tuesday, and a number of them have died.

Autopsies on victims in Turkey shortly after the attack, monitored by the World Health Organization, had concluded there was evidence of sarin exposure.

The results of the tests in Turkey, if true, will add fuel to accusations by western powers that the Assad regime deployed sarin in one of the most devastating mass casualty chemical attacks in the six-year conflict.

The US secretary of state, Rex Tillerson, said there was “very high confidence” that sarin was used in the attack and that it had been carried out by forces loyal to Assad.

Russia, Assad’s principal backer in the war, has said the air raids targeted a rebel warehouse that contained chemical weapons that then leaked out to the surrounding area.

A visit by the Guardian to the site of the chemical attack on Thursday found no evidence to back the Russian claim, and instead found an empty, abandoned warehouse and grain silos that were empty except for soil and animal feed.

The Russian president, Vladimir Putin, on Tuesday said western and Turkish accusations that Syria’s government dropped the nerve agent sarin that killed dozens of civilians in Idlib were comparable with discredited claims that Saddam Hussein had stockpiled weapons of mass destruction in Iraq.

“It reminds me of the events in 2003 when US envoys to the security council were demonstrating what they said were chemical weapons found in Iraq,” he told reporters. “We have seen it all already.”

The chemical attack prompted a major change in US policy on Syria and a departure from that of the previous administration, which had refused to directly engage the Assad regime militarily. After indicating prior to that attack that Assad’s removal was no longer a priority, the US launched 59 Tomahawk missiles on the Syrian air base where the chemical attack was launched from.

Top US officials have since said they see no political solution with Assad in power.