Indonesia's anti-terrorist squad arrested 11 suspected Islamic militants it said planned to attack the U.S. embassy, a plaza near Australia's embassy and the offices of Freeport-McMoRan Copper & Gold, a police spokesman said on Saturday.

The Detachment 88 squad seized bomb-making equipment and one bomb ready to be used by a new militant group called Harakah Sunni for the Indonesian Society (HASMI), said National Police spokesman Suhardi Alius in a statement.

The arrests by the elite police squad on the island of Java were the latest step in a crackdown by authorities against militants during which dozens have been arrested and at least seven killed.

They come 10 years this month after a bomb attack on Bali killed 202 people, most of whom foreign tourists.

"The first piece of evidence was found at a housing complex in Madiun (Java), a bomb ready to detonate, as well as raw materials for bomb making and instruction books on how to make bombs," Alius said, before listing other evidence of explosives.

He gave no further details about the group's identity.

He listed targets as the U.S. consulate in Surabaya, East Java, its embassy in Jakarta, Plaza 89 in Jakarta, which is in front of the Australian embassy, and the offices of mining company Freeport.

HASMI also planned to attack the Mobile Police Brigade in the central Java city of Srondol, he said.

"We have seen the reports, but cannot comment as this is an ongoing Indonesian security investigation," a State Department spokeswoman in Washington said in an emailed statement to Reuters.

A spokeswoman for the U.S. Defence Department said she was unaware of any request by the State Department to increase security at its embassy in Jakarta in response to the reported arrests.

The Bali bombings, which in turn came just over a year after the September 11 attacks on the United States, were a watershed for Indonesia, the country with the world's largest population of Muslims.

They forced the secular state to confront the presence of a small but dedicated group of followers of Osama bin Laden bent on attacking Western targets.

After 2002, Indonesian forces worked with Australia and other countries to crack down on the al Qaeda-linked Southeast Asian militant group Jemiah Islamiah that was behind the bombs.

The hunt led to the arrest of hundreds of militants. Many were killed in shootouts and the three main perpetrators of the bombings were convicted and executed by firing squad in 2008.