Prime Minister Theresa May has said the UK would "never intentionally strike or focus on Syrian forces", after Britain confirmed it took part in air strikes that killed dozens of Syrian troops.
Mrs May explained that the UK was working as part of a coalition against the Islamic State group in Syria.
At least 62 Syrians were killed in the strikes, as the US said it may have accidentally hit a government position.
Mrs May said the UK would now contribute "fully" to an investigation.
Speaking at the UN headquarters in New York, she said: "We are now part of the investigation and it's right that this is properly investigated.
"But, from the UK's point of view we are there to deal with Daesh, to deal with the terrorist threat that is Daesh."
Mrs May was attending the UN's summit for refugees and migrants where she urged the international community to "come together" to deal with the Syrian crisis.
The Ministry of Defence has confirmed that an unmanned RAF remotely-piloted Reaper drone took part in the Deir al-Zour strikes.
US, Australian and Danish aircraft were also involved.
The US has already expressed "regret" for the "unintentional loss of life", while Australia's Department of Defence has offered its condolences to the families of government soldiers killed or wounded.
A Syrian army source said the air strike had allowed IS to gain ground in the area around the Syrian airbase, but that Syrian forces had regained most positions on the hilltop nearby with the help of Syrian and Russian air support.
The attack dealt a further blow to the ceasefire deal, which was agreed by the US and Russia on 12 September but declared over by the Syrian military on Monday evening.
The US, which brokered the seven-day deal with Russia, said it was working to extend the agreement.
The US and Russia are to hold further talks on the Syrian situation in New York on Tuesday, the state department added.
In Syria, the US-led air campaign began in September 2014.
The UK carried out its first air strikes against IS in Syria in December 2015, after MPs overwhelmingly backed military action in a parliamentary vote.
Since then, more than 4,900 strikes have been carried out by coalition forces, which include Australia, Bahrain, Canada, France, Jordan, the Netherlands, Saudi Arabia, Turkey, United Arab Emirates and the UK.
At the UN summit in New York, Mrs May also called for greater international efforts to tackle slavery.
She said the heads of MI5, MI6 and GCHQ would be part of a new taskforce looking at ways to combat the modern-day slave trade in the UK, with representatives from international law enforcement agencies Europol and Interpol also attending meetings.
The government has earmarked £33m from the UK aid budget to tackle modern slavery in high-risk countries from which victims are regularly trafficked to the UK, with at least £5m due to be spent in Nigeria.
The prime minister also called for a "radical new approach" across borders, similar to that use to combat drugs trafficking and illegal firearms.
"We owe it to the innocent men, women and children who are being tricked into a life of hard labour and abuse to rid our world of this evil," she added.