South Africa had taken a "welcome" principled stance in voting for United Nations resolution on the unrest in Syria, British Foreign Secretary William Hague said on Tuesday.

Speaking in Cape Town, Hague said people were dying in Syria because the UN Security Council (UNSC) had failed to agree on a united response on the assault against protesters by the forces of Syrian President Bashar al-Assad.

"We welcome the principled stance that South Africa took in voting, as we did, for the UNSC resolution," Hague said.

"I welcome the discussions that I have had with your Foreign Minister [Maite Nkoana-Mashabane] yesterday [Monday] about intensifying peaceful diplomatic pressure and supporting the regional leadership shown by the Arab League."

He said Britain and South Africa agreed about wanting Syrians to be allowed to resolve their differences peacefully.

"What currently stands between them and this legitimate aspiration is the Assad regime's naked determination to cling to power at any cost," Hague said.

"That is why we are determined to use every peaceful means to intensify the diplomatic and economic stranglehold on the regime."

Hague said the world faced a danger of nuclear arms being acquired by new states "who may not be that responsible in developing them and in harbouring the technology without selling it to others".

The danger was not necessarily of Iran developing nuclear weapons capability, but of several other countries in the Middle Eastern region doing the same in response, he said.

"We could end up with the world's most unstable region politically in possession of the world's most dangerous weapons. I think what is crucial is that we prevent proliferation."

Hague said that while it was right that countries such as South Africa took their place at the "top table" in world affairs, it was up to African countries to decide who would represent them as a possible permanent member of the UNSC.

He said Britain supported the reform of the UNSC, which reflected the outcome of World War Two.

"We think there should be an expanded security council with more permanent members," he said in answer to a question on whether Britain would back South Africa's bid for a permanent seat on the council.

"It is for countries of Africa to determine the nature of that representation. I don't think it is for the rest of the world to determine that."

He said Britain was active in supporting South Africa's efforts in finding a political solution in Zimbabwe.

"We see South Africa and [the Southern African Development Community] as leading the way," he said.

Britain would continue to help Zimbabwe with its UK80 million development fund.

"We will help in other ways," Hague said.