Internet and mobile-phone networks were reported down in Syria and flights out of Damascus were restricted as fighting moves closer to the nation's capital.
Members of the Friends of the Syrian People International Working Group met Friday in Tokyo to discuss steps to isolate the Assad government and its supporters.
The British government, which had representatives in Tokyo, said the panel adopted a measure condemning "in the strongest terms" gross violations of human rights committed in Syria.
"The group renewed its commitment to those sanctions already in place and called for all states to adopt further sanctions targeted against the Assad regime and its supporters," a statement from the British government read.
London recently recognized an opposition Syrian council as the legitimate representative of the Syrian people. U.S. Ambassador to Syria Robert Ford was quoted by CNN as saying Thursday that Washington was taking a wait-and-see approach to the Syrian council.
"We would like to see them continue to develop as an organization, as a coalition that are making real progress and I expect that our position with them will evolve as they themselves develop," he said.
Joint U.N.-Arab League special peace envoy for Syria, Lakhdar Brahimi, said following a meeting at the United Nations that there's no sign that an internal solution will resolve the crisis.
"The situation in Syria is bad, and it bears repeating, it is getting worse," he said.