By Kylie MacLellan
LONDON (Reuters) - Britain is looking at its military options in Syria but any action would need to be part of a coalition involving the United States and is not likely to happen soon, foreign minister Boris Johnson said on Thursday.
Prime Minister Theresa May's spokeswoman took a more cautious approach, saying there were no plans for further military action and no decisions had been made.
But Johnson's comments reflected frustration, shared in other Western capitals, at the worsening humanitarian situation in Syria and what he described as the barbaric role of Russia alongside the forces of President Bashar al-Assad.
"It is right now that we should be looking again at the more kinetic options, the military options," Johnson told a committee of lawmakers. "But we must be realistic about how these in fact work, and what is deliverable."
"We can't do anything without a coalition, without doing it with the Americans. I think we're still a pretty long day's march from getting there but that doesn't mean that discussions aren't going on, because they certainly are."
The British government failed to win parliament's support in 2013 for a plan to bomb Assad's forces to punish him for using chemical weapons. But it has been involved in air strikes against Islamic State in Syria since winning the support of lawmakers last December.
May's spokeswoman said the government was looking at a range of options as it seeks to help bring an end to more than five years of civil war in Syria.
"We need to think through carefully the consequences of any action," she said. "We are talking to partners about is there any more we can be doing to end this appalling conflict."
Renewed bombing of rebel-held eastern Aleppo has killed more than 150 people this week, rescue workers said, as the Syrian government steps up its Russian-backed offensive to take the whole city. Syria and Russia blame their foes for breaking a ceasefire and say they target only militants in the city.
Johnson said it was important not to raise false hopes over the idea of a no fly zone over parts of Syria to prevent the Russian and Syrian government air strikes on Aleppo.
"We know the difficulties and implications of a no fly zone or a no bombing zone," he said. "But if there is more that we can reasonably and practically do together with our allies, then of course we should consider those measures."
Russia said it would welcome Britain's involvement if it targeted terrorists rather than Assad's forces.
Johnson, who said another option was to intensify sanctions on key players in Assad's administration, said he would host a meeting between U.S. Secretary of State John Kerry and European foreign ministers in London on Sunday to discuss the situation.
Kerry and Russian Foreign Minister Sergei Lavrov are due to attend a meeting in Lausanne on Saturday for talks on Syria.
(Additional reporting by William James; Editing by Mark Trevelyan)