* EU to adopt fresh Syrian sanctions - Westerwelle
* Germany, U.S., UK urge Russia and China to rethink
* Clinton says Russia and China making wrong choices (Adds Clinton, details, background, quotes)
By Dave Graham
LOS CABOS, Mexico, Feb 20 (Reuters) - The European Union will likely adopt fresh sanctions against the government of Syrian President Bashar al-Assad in the coming week, German Foreign Minister Guido Westerwelle said on Monday.
Germany and other Western powers have repeatedly called on Assad to step down to put an end to protests against his government, which have triggered a violent backlash from his security forces.
Syrian security forces have killed more than 5,000 people in the past year, according to human rights groups, while the Assad government says more than 2,000 soldiers and security agents have been killed.
"We will adopt further sanctions in Europe, and not just in Europe," Westerwelle told Reuters in an interview on the sidelines of a meeting of foreign ministers from the Group of 20 economic powers in Los Cabos, Mexico.
"I believe sanctions will be tightened in the next week, because the violence is continuing," he said, when asked whether Europe would adopt measures to blacklist Syria's central bank.
Westerwelle declined to name specific sanctions under consideration, but a G20 official at the meeting, speaking on condition of anonymity, said the EU was on course to agree to measures to curb the central bank's ability to operate.
EU diplomats said this month they were working on a new round of sanctions against Syria, which they hope to finalize by Feb. 27. These would include a freeze on the Syrian central bank's assets as well as on most transactions with it.
Westerwelle said it was time to raise diplomatic pressure against Syria, and received support from the United States and Britain in Mexico, who also urged China and Russia to do more.
"We'll send a clear message to Russia, China and others who are still unsure about how to handle the increasing violence, but are up until now unfortunately making the wrong choices," U.S. Secretary of State Hillary Clinton told reporters.
Beijing and Moscow angered the West and Arab states this month when they vetoed a draft U.N. Security Council resolution that backed an Arab plan demanding Assad step aside.
On Monday, the two powers showed support for Assad.
Assad met a senior Russian politician in Damascus, who reiterated Moscow's backing for his self-styled reform program and spoke out against any foreign intervention in the conflict, Russian and Syrian news agencies reported.
China accused Western countries of stirring up civil war in Syria and two Iranian warships docked at a Syrian naval base, underscoring rising international tensions over the crisis.
Westerwelle said he expected a meeting in Tunisia organized by the Arab League later this week to strengthen the hand of the Syrian opposition, which is hoping for official recognition as a government-in-waiting.
Clinton said the Feb. 24 meeting in Tunisia of the "Friends of Syria," organized by the Arab League to build international momentum against Assad, would help weaken Assad's government.
"Like the U.N. general assembly resolution that passed overwhelmingly last week, the upcoming meeting will demonstrate that Assad's regime is increasingly isolated and that the brave Syrian people need our support and solidarity," she said.
"We have to prepare for the likelihood that the Syrian regime is going to be under increasing pressure which will create perhaps more space for all of us to push hard on a transition, and we will intensify our diplomatic outreach to those countries that are still supporting the Assad regime."
Arab countries will encourage the Syrian opposition to unite before they formally recognize them as a government-in-waiting, Tunisia's government said as it prepared to host the meeting.
The Syrian National Council (SNC) has emerged as the international voice of the uprising but has yet to show a real command over grassroots activists and an armed insurgency.
British Foreign Office minister responsible for relations with Latin America, Jeremy Browne, said Assad's government no longer reflected the will of its people and urged dissenters in the U.N. Security Council to provide a solution to the problem.
"We'd like to see the Russians and Chinese come forward with more suggestions on how we can bring about peace in Syria," he said. "The regime is existing on borrowed time." (Additional reporting by Andrew Quinn and Krista Hughes; editing by Todd Eastham)