Turkey has called on the US, Britain and other leading countries to take immediate action to intervene in Syria to prevent a looming humanitarian "disaster" that it says threatens the lives of millions of internally displaced people and refugees as winter approaches and could soon ignite a region-wide conflagration.

Appealing to the major powers to set aside their differences over how to end the 20-month-old civil war in which an estimated 32,000 people have died, Ahmet Davutoglu, Turkey's foreign minister, said the crisis had gone on for long enough. The Syrian people were crying out for help and their pleas could no longer be ignored.

"How long can this situation continue? I mean in Bosnia, now we have Ban Ki-moon [the UN secretary general] apologising 20 years after. Who will apologise for Syria in 20 years' time? How can we stay idle?" Davutoglu told the Guardian in an exclusive interview in Istanbul.

"We [Turkey] are doing all we can to help these people, using all diplomatic capacity to stop this bloodshed. But there should be a much more concerted effort by the international community. The best way we can see now is direct humanitarian intervention."

The call came as the UN's peace envoy, Lakhdar Brahimi, travelled to Damascus for crucial talks with the regime due to be held on Saturday – the latest bid, after several failed international initiatives, to bring a halt to the killing. Brahimi is expected to propose a temporary truce, beginning on 26 October, the start of the Eid al-Adha holiday, in the hope that it may lead to a permanent ceasefire.

Predominantly Muslim Turkey, a leading Middle East power that is also a Nato member and long-time US ally, has been caught in the storm as the Syrian crisis has unfolded south of its shared 560-mile (900km) border. Opinion polls show most Turks are fearful of their country being sucked into the Syrian quagmire.

More than 145,000 refugees have taken shelter in improvised camps or Turkish cities, fighters of the Free Syrian Army and their Gulf backers use Turkey as a base and covert weapons supply route, and fighting has spilled on to Turkish soil.

Earlier this month, Syrian shelling killed five Turkish civilians in the town of Akçakale, triggering a week of cross-border artillery and mortar exchanges and fears of all-out war. Turkey also recently forced down an aircraft flying from Russia to Syria that it said was carrying military equipment.

Turkey's earlier proposal to the UN to set up a border buffer zone, backed by a possible no-fly zone, was ignored by the US, Britain and other Nato members wary of involvement in another Middle East war. Russia and China oppose direct intervention.

Now, clearly frustrated by the impasse and deeply concerned at the prospect of a spreading conflict, Turkey's leaders appear to be adopting a tougher line while appealing to the world's conscience.

The Syrian regime's continuing use of air bombardment and heavy weapons against Syria's civilian population was propelling the country and the region towards a human catastrophe, Davutoglu said. A much more robust response was required from London, Washington and Paris.

"If nothing is done, maybe in the next two months it [the number of refugees] will double to 200,000, even 400,000 … When the technology the regime was using was snipers, the refugees were coming in a few thousands. Now they are using artillery shells and tanks, the number increased rapidly," Davutoglu said.

"We want the international community to find a solution to resolve this issue inside Syria. All means can be discussed. But there must be proper humanitarian access. We have 145,000 refugees in Turkey but there are millions of people, two million people inside Syria who are IDPs [internally displaced people]. Those that are lucky can come to Turkey. They are the lucky ones.

"So there has to be humanitarian access, a humanitarian mission inside Syria, and the international community must be ready to protect it. This is the question, whether it is a buffer zone or humanitarian access – how these people are to be protected inside Syria. We are calling for an international humanitarian mission to go into Syria and be protected to stop the refugee flow.

"The international community must make a decision. Humanitarian access must be guaranteed by any means that is acceptable. These people are human beings. The winter is approaching. How will they survive the winter?"

Davutoglu stressed any new initiative must be backed by the UN security council. If it established a mechanism to guarantee international humanitarian assistance inside Syria, Turkey would support it and would allow its soil to be used as a base. But Turkey would not act alone or without UN authorisation, he said.

Alluding to the Obama administration, which has been criticised by Republicans for a weak response, as well as to Britain and other countries, Davutoglu said: "We expect the leading powers of the international community to be more firm, more decisive and clear in their policy regarding oppression in Syria."

Davutoglu said Turkey was not seeking military confrontation with the regime of President Bashar al-Assad. But the international community must send a "stark warning", via the UN security council, that some of Damascus's actions constituted a "war crime", he said. Turkey wanted the immediate creation of a transitional government, leading to democratic elections. If Assad wanted to avoid facing war crimes charges in The Hague, he should stop killing his own people.

While Recep Tayyip Erdogan, Turkey's prime minister, has called for Assad to step down, Davutoglu said it was ultimately a matter for the Syrian people.

"It is not our business, it is for them to decide. But after such a criminal act, such oppression and aggression, more than 30,000 people have been killed, we don't know how many are lost, millions are IDPs, and maybe more than 500,000 are refugees, how can such a person [Assad] who is responsible for these statistics continue to run a country?"

With Brahimi due in Damascus, Davutoglu said Turkey would support a meaningful peace process in Syria but its end objective must be a transfer of power.

The biggest problem for any talks process was that Assad could not be trusted to keep his word, Davutoglu said. Turkey has suggested that Faruk al-Shara, Syria's vice-president, might lead any transition negotiations. This idea was predictably rejected by Damascus, and by its main regional ally, Iran.

"We don't see a serious counterpart in Damascus for such talks who is powerful or strong enough to fulfil commitments … Last year myself personally and other senior state officials went to Damascus to convince the regime to halt the violence against civilians. But unfortunately they did not fulfil their promises.

"What is the purpose of any dialogue if it legitimises the Syrian regime? If they are sincere, there are channels to have a dialogue, UN special envoy Brahimi and many other channels. If they come to us with a proposal to end the bloodshed and allow the people to decide their own future, then there will always be a channel."

Davutoglu said he was hopeful that Russia, wary of another Libyan-style, regime-changing Nato operation, might be persuaded to soften its anti-interventionist stance, once the scale of the impending humanitarian crisis became clear.

"I have contact with [Sergei] Lavrov [Russia's foreign minister]. They have their own approach especially after the Libyan experience, but even if there was a mistake or something wrong in Libya and I don't think that there was, why should Syrian people pay the price?"

Asked about US concerns that hardline jihadi groups were hijacking Syria's uprising, Davutoglu said that possibility made a swift solution all the more urgent.

"The presence of some groups on the ground should not be used as an excuse for not being active. Prolonging the crisis will create a much more critical environment concerning these groups. We must have a solution and act as soon as possible to avoid a power vacuum in Syria.

"We must immediately establish a transitional government and let the Syrian people see a light at the end of the tunnel. At present they do not see light at the end of the tunnel. In the surrounding darkness, anyone can do anything."