Daniel Ellsberg, Ann Wright, Other Activists Arrested at Bradley Manning Protest

Dozens of activists, including the man who leaked the Pentagon Papers on the Vietnam War, were arrested Sunday at a military base holding the US soldier suspected of leaking secret US cables, supporters said.

"It was a strong showing of a cross section of Americans who support Bradley Manning and oppose his unconstitutional confinement," said Kevin Zeese, an attorney with the Bradley Manning Support Network, in a statement.

Manning "is being selectively prosecuted, pure and simple," said Zeese.

Whistleblower Daniel Ellsberg of Pentagon Papers fame and retired US colonel Ann Wright were among 30 activists detained amid the peaceful demonstration at the Quantico Marine base in Virginia, according to the group.

The pair, said supporters, were "arrested as they approached the gates of the base in an attempt to deliver a letter" to the Quantico base commander Daniel Choike.

Manning, 23, was arrested in June while deployed to Iraq amid suspicions he had passed a trove of secret US government documents to WikiLeaks, the whistle-blowing website, many of which were then published around the world.

On March 2, the US military unveiled 22 additional charges against Manning including the serious offense of "aiding the enemy," which carries a potential death sentence. But the army said he would face possible life in prison.

Ellsberg, who as a government consultant leaked the Pentagon Papers that revealed war planning in Vietnam, has previously saluted Manning.

"I'm afraid that will happen indefinitely unless more people follow the example of Bradley Manning, whose courageous act of civil disobedience probably confronts him with life in prison," Ellsberg said to a crowd of supporters at a rally earlier this month.