(Adds claim of responsibility paragraph 5)

GAZA, Sept 11 (Reuters) - Two bombs exploded on Thursday near Israeli troops patrolling the border with the Hamas-ruled Gaza Strip, causing no injuries, in the first such incident since a ceasefire took hold in June.

The first blast occurred near an Israeli army vehicle and caused damage to the border fence, an army spokeswoman said.

A Gaza witness said an Israeli ambulance was at the scene, at the border between Israel and the central Gaza Strip, but the army said nobody was injured.

A second explosion went off minutes later in the same area, but also caused no injuries, the army said.

The previously unknown "Attawheed Brigades" militant group claimed responsibility for the attack, saying it was in response to Israeli violations of the ceasefire agreement.

The incident could undercut an Egyptian-brokered ceasefire between Israel and Hamas Islamists who seized control of the Gaza Strip more than a year ago.

The truce has largely held since it took effect on June 19, halting fighting, though both sides accuse the other of sporadic violations. (Reporting by Nidal al-Mughrabi in Gaza and Avida Landau in Jerusalem; Writing by Adam Entous; Editing by Matthew Jones)

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