Syrian rebels are set to meet US Secretary of State John Kerry and other G8 foreign ministers gathered in London on Wednesday, with nuclear fears over North Korea and Iran also high on the agenda.

Rebel prime minister Ghassan Hitto and Syrian National Coalition vice presidents George Sabra and Soheir Atassi are expected to push their demands for weapons to help topple President Bashar al-Assad.

The meeting of the top diplomats from the Group of Eight leading industrialised nations will also tackle Myanmar, Somalia, cyber-security and the issue of preventing sexual violence in war zones,

"Literally, the top of our agenda will be the situation in Syria, that will be the first subject that we discuss," British Foreign Secretary William Hague said in a briefing on Tuesday.

Hague said he had discussed the issue of arming the rebels with the three visiting Syrian opposition figures on Tuesday.

"They will be able to meet with some of the G8 foreign ministers (on Wednesday) before the G8 fully gathers" for a ministers' dinner followed by full talks on Thursday, he said.

Russian foreign minister Sergei Lavrov was highly unlikely to be among those meeting the Syrian opposition representatives given Moscow's support for the Assad regime.

Syria's opposition umbrella group the National Coalition is recognised by the United States and many other Western and Arab countries as the sole representative of the Syrian people.

The Syrian opposition was formally granted an Arab League seat last month.

Kerry, who touched down in London late Tuesday, said that with the rebels he would be "discussing various means of having an impact on President Assad's calculations about where the battlefield is going."

Asked if Washington might step up help to Syrian rebels including military aid, Kerry said it was "up to the White House to make any announcement."

But Hague said Britain and France would continue to push for the lifting of an EU arms embargo to Syria so they can arm the rebels. The embargo is due to expire at the end of May but other EU nations are largely in favour of renewing it.

The United Nations says the Syria conflict, now in its third year,has claimed more than 70,000 lives.

Iran, Syria's main ally, will also loom large at the G8 talks after nuclear negotiations between Tehran and world powers ended in deadlock at the weekend.

Hague said it was "not helpful at all" that Iran had unveiled a new uranium production facility and two extraction mines days after the talks held in Kazakhstan, and said the G8 ministers would "take stock" of the situation.

The so-called group of P5+1 -- comprising the United States, Britain, France, China and Russia plus Germany -- are engaged in a diplomatic effort to convince Iran to curb its nuclear activities in return for some sanctions relief.

But Hague added that "we're not suggesting today additional sanctions on Iran."

The spiralling tensions over North Korea would also be a key topic, with Wednesday being the point Pyongyang had previously said beyond which it could not guarantee the safety of foreign diplomats on the grounds that war may break out.

"We will be able to discuss the rhetoric of the DPRK and any action that they take. We've been very clear that if it carries out any further provocations it will be met with a robust international response," Hague said.

"Talking about the choice that faces Iran, there is an important choice facing North Korea," he said.

The Korean peninsula has been locked in a cycle of escalating military tensions since the North's third nuclear test in February, which drew toughened UN sanctions.

Hague meanwhile said his "personal priority" for the meeting was a new agreement to prevent sexual violence in conflicts.

The G8 foreign ministers -- from Britain, Canada, France, Germany, Italy, Japan, Russia and the United States -- hold a dinner on Wednesday and formal talks on Thursday.

Britain, which holds the rotating chairmanship of the group this year, will host a G8 leaders summit in Northern Ireland in June.