John Kerry has indicated the United States is prepared to step up its assistance to the Syrian opposition movement, following the latest deadly rocket attack on the northern city of Aleppo.

Speaking during a joint press conference in London with foreign secretary William Hague on Monday afternoon, the secretary of state told reporters to "stay tuned" for an announcement after a planned summit in Rome this week.

"I haven't said anything about what we are specifically planning to do," Kerry said. "We really owe it to friends and allies to discuss those things with them first, I do not think they should be reading about positions in the newspapers, there will be a moment for our decision that moment is after we have a meeting in Rome."

It has been reported that the Syrian opposition movement is undecided about whether to attend the international conference in Italy, but Kerry urged it to send representatives.

"We are not coming to Rome simply to talk, we are coming to Rome to make a decision about next steps and perhaps other options. Stay tuned."

"The Syrian people want to see results from this conference," he added. "So do we."

"The best way to get those results is to join us, be part of this discussion. What has happened in Alepo in the last days is unacceptable."

Speaking alongside Kerry, Hague said British policy towards Syria "can not be static" given the "terrible human costs" and the "mounting danger of instability in neighbouring countries".

Kerry made the comments at the start of his first foreign tour as President Obama's new secretary of state. The trip, which began in London where he met David Cameron as well as Hague, will also take in Berlin, Paris, Rome, Ankara, Cairo and Riyadh.

SEE ALSO: John Kerry And David Cameron Avoid Falklands And EU Exit During Meeting

Related on HuffPost: