Leaders from across the world have called for an impartial investigation into a suspected chemical weapon attack in Syria, stating that unilateral action by the US increases the risk of terrorism.

Following the attack in Khan Sheikhoun on 4 April, the US pinned sole responsibility on Syrian President Bashar Al-Assad and conducted retaliatory missile strikes from two navy warships.

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However, countries including Iran, China and Bolivia said an independent probe needs to be carried out to establish who was responsible before further action was taken. The Syrian government has insisted it had no part in the attack.

In a speech on Saturday (8 April), Iranian President Hassan Rouhani said: "We are asking for an impartial international fact-finding body to be set up… to find out where these chemical weapons came from," reported Reuters.

Rouhani's statement alluded to intelligence that suggests other actors in Syria, such as the Al Qaeda-linked Jabhat Al-Nusra, also had access to chemical weapons.

In a series of tweets, he also said: "The tragedy of Khan Sheikhoun is horrifying and must be condemned. It reminds Iranians, victim of chemical weapons for years, the attacks in Sardasht.

"US aggression against Shayrat strengthens regional extremism and terror, and global lawlessness and instability, and must be condemned.

"I call on the world to reject such policies, which bring only destruction and danger to the region and the globe."

China's statement on the attack also voiced its condemnation but stressed the importance of independence.

Hua Chunying, foreign ministry spokesperson, said in a statement: "China supports the United Nations in launching an independent and comprehensive investigation on the issues in order to come to a conclusion that stands the test of history and reality.

"China called on all sides to prevent the deterioration of the situation in order to ensure the political solution in the Syria crisis."

At an emergency UN Security Council on the suspected chemical weapon attack, Bolivia decided to take less of a diplomatic approach. The country's representative to the UN Sacha Llorenti evoked former US Secretary of State Colin Powell's infamous 2003 presentation to the body in which he asserted Iraq had weapons of mass destruction.

"Now the United States believe that they are investigators, they are attorneys, judges and they are the executioners," Llorenti said.

"That's not what international law is about.

"I believe it's vital for us to remember what history teaches us and on this occasion [in 2003], the United States did affirm, they affirmed that they had all the proof necessary to show that Iraq had weapons of mass destruction but they were never found… never were they found."

Scotland's First Minister, Nicola Sturgeon, also criticised the cruise missile strike.

Speaking on BBC Radio Scotland's Good Morning Scotland, Sturgeon said, "My doubt and my scepticism about simply dropping bombs is that it doesn't necessary take us one single inch closer to that peaceful outcome."

However, Sturgeon followed the British government's line by blaming Assad for the attack:

"What I understand is the instinct to do something in the face of the quite horrific chemical attack carried out by the Assad regime earlier this week. That regime is completely beyond the pale. So there is in these circumstances I think always a sense of wanting to hit back and to do something."

The politician, who recently returned from a five-day long visit to the US, went on to criticise US action for not acting to preserve peace in Syria, but adding to the chaotic situation the country faces.

"My concern about air strikes is and always has been that they are no substitute for a real plan for peace and what we need to see in Syria is an end to the conflict, the multifaceted, horrible conflict that is under way in that country," said Sturgeon.

"I suppose I have a concern that air strikes, particularly given what appears to be the quite dramatic change in the position of the American administration, increases the uncertainty and the unpredictability of the situation in Syria. "There must be the focus on trying to find a peace that is sustainable in Syria."