The U.S. embassy in Iraq cautioned its citizens that there may be unrest during a referendum on independence planned by the Kurdish authorities in northern Iraq, opposed by the central government in Baghdad.

"In particular, U.S. citizens should avoid travel into and within territories disputed between the Kurdish Regional Government (KRG) and the Government of Iraq," the travel warning said.

The KRG has resisted calls by the United Nations, the United States and Britain to delay the referendum. Iraq's powerful neighbours, Iran and Turkey, strongly oppose the vote as they fear could fuel separatism among their own Kurds.