Representatives of more than 70 countries and organizations are gathering outside the Tunisian capital, Tunis, for a conference Friday aimed at supporting the Syrian opposition. Getting aid to civilians caught up in Syria's violence will be high on the agenda.

The officials are gathering for the first meeting of what is now called the Friends of the Syrian People -- a movement that came in reaction to the Russian and Chinese vetoes of a United Nations Security Council resolution that would have condemned the Syrian government.

The group lacks the Security Council's authority, but hopes to use a combination of pressure and persuasion to convince Syrian President Bashar al-Assad to allow humanitarian aid and agree to end his family's more than 30-year monopoly on power.

It will be a difficult task. Mr. Assad already has defied the Arab League, which is a leader of the movement, and the U.N. General Assembly -- intensifying his military campaign against pro-democracy activists that unofficial reports say has killed thousands of civilians.

En route to the Tunis meeting, U.S. Secretary of State Hillary Clinton said Thursday the conference will reflect the international consensus for change in Syria, and that she hopes it will put enough pressure on the Syrian leader to convince him to change.

"We see a lot of developments that we think are pointing to pressure on Assad. We hope it'll pressure him to make the right decision regarding humanitarian assistance. But in the event that he continues to refuse, we think that the pressure will continue to build. So it's a fluid situation. But if I were a betting person for the medium-term and certainly the long-term, I would be betting against Assad," Clinton said.

A senior State Department official traveling to the conference with the secretary told reporters that participants will issue a challenge to President Assad to allow international aid into areas his troops have cut off from the outside world while residents suffer daily artillery barrages. The official, speaking on condition of anonymity, said the conference will also express support for the Arab League transition plan for Syria that would replace Mr. Assad with a council and lead to elections. He said it will also expand ties with the main opposition group, the Syrian National Council, and will seek ways to increase pressure on the Assad government through better focused and coordinated sanctions.

The official would not say whether the gathering will discuss arming Syrian opposition forces in the border areas. But he said it might agree to provide some communications equipment to counter the government's cutoff of telephone and Internet networks. He said Secretary Clinton discussed such moves with her counterparts in London on Thursday on the sidelines of a meeting about the Somalia crisis.

Clinton said that Friday's conference is aimed in part at Syria's key supporters.

"The pressure will build on countries like Russia and China because the world opinion is not going to stand idly by. Arab opinion is not going to be satisfied, watching two nations -- one for commercial reasons, one for commercial and ideological reasons -- boost a regime that is defying every rule of modern international norms," she said.

Officials say they hope a unified international approach and an engaged Syrian opposition movement will convince President Assad to change his policies. But some opposition members say Western and Arab countries must moderate their approach, and bring China and Russia into the process, if they are to have any chance of ending the violence and achieving political change in Syria.