CANBERRA, Oct 6 (Reuters) - Australia will stop detaining asylum seekers in Papua New Guinea (PNG) at the end of December, the two countries said on Wednesday, as Canberra shuts one of two remote Pacific detention centres that have been criticised by the United Nations. Under Australia"s hardline immigration policies, asylum seekers attempting to reach the country by boat have since 2013 been sent to detention centres on PNG"s Manus Island and the South Pacific island nation of Nauru. "The Australian government regional processing contracts in PNG will cease on 31 December 2021 and will not be renewed," a joint statement read. PNG had been pressing Australia to close the centre. At its peak, Australia detained about 1,000 men on Manus Island and while most have left, advocates said just over 100 remain as they either await resettlement to a third country or have had their asylum seeker applications refused. Australia said those who will remain can transfer to Nauru or stay in PNG where they can seek citizenship. Australia and Nauru earlier this year extended an agreement to allow asylum seekers to continue being held on the tiny island. The United Nations and aid agencies have criticised conditions on Manus and Nauru, citing human rights abuses and called for their closure.