Vietnam police swoop on anti-China protest, 20 detained HANOI (Reuters) - Police in Vietnam moved swiftly to break up an anti-China protest on Sunday, making at least 20 arrests in the latest sign of the communist regime's tough stance on dissent, and even after it chided Beijing for aggression in the South China Sea. As crowds gathered in response to the recent ramming of a Vietnamese trawler by Chinese navy vessels, uniform and plain clothes police blocked off rallying points and quickly put protesters on to waiting buses, Reuters witnesses said. Two Vietnamese journalists working for foreign media were also detained at the protest near Hanoi's Hoan Kien lake. Vietnam's has been criticized by Western countries including the United States for crushing freedom of speech and arresting its detractors as discontent grows over land grabs, graft and the state's management of an economy hamstrung by bad debt. Diplomats and experts say the ruling party is eager to curtail all protests, even those against rival China which it once tolerated, fearing they could mushroom into wider anti-government movements. Tensions in the decades-old territorial dispute have risen in recent weeks after Chinese vessels struck a Vietnamese fishing boat and later converged near a ship the Philippines ran aground on a reef in 1999 to mark its territory. The Philippines warned China to withdraw from what Beijing considers its "indisputable territory" and Vietnam complained of a "serious violation" of its sovereignty. In a rare break from a usually diplomatic tone, Vietnam Prime Minister Nguyen Tan Dung on Friday warned of damage to regional economies and global trade if "unilateral might, groundless claims" and "power politics" were to ignite a conflict in the South China Sea. Dung made the comments during an address to the Shangri-La Dialogue in Singapore but did not specifically name China. Reporting by Martin Petty; Editing by Michael Perry