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By Josiane Kouagheu
DOUALA (Reuters) - Gunmen attacked a border crossing in Cameroon's southwest on Thursday, launching their assault from Nigeria, security source witnesses said.
No one was killed, the officials said, but the incident is likely to further damage relations between the neighbours, strained over the rise of an Anglophone Cameroonian separatist movement.
Five security and administrative agents said the unidentified gunmen launched their attack on the Ekok border post along Cross River.
"They came around 3 a.m. (0200 GMT). They came from Nigeria and there were many of them. They had heavy weapons. They had grenades. They were shooting everywhere," said one police source, who like the other witnesses asked not to be named.
He said the shooting lasted nearly three hours and the border remained closed on Thursday morning.
"We don't really know how it happened," a second security source told Reuters. "Some of these guys came from the riverside (beneath the bridge). We don't know exactly which path they took, but all of them came from Nigeria."
Government officials in Cameroon would not immediately comment on the attack.
Nigeria's defence ministry spokesman said he was not aware of the incident and referred queries to the military. A Nigerian military spokesman said he was not aware of the attack but would make checks.
Cameroonian military officials and pro-government media accuse Nigeria of sheltering the insurgents, who since last year have waged a guerrilla campaign to establish an independent homeland for Cameroon's English-speaking minority.
Reuters reported last month that Cameroonian troops crossed into Nigeria in pursuit of the rebels without seeking authorisation from Nigeria, provoking a behind-the-scenes rift between two nations with a history of fraught relations.
The militaries of Cameroon and Nigeria repeatedly clashed over the disputed Bakassi peninsula in the 1980s and 90s.
The status of the territory was settled in Cameroon's favour by The Hague-based International Court of Justice in 2002 and in recent years the two countries have cooperated extensively to stamp out the Islamist militant group Boko Haram.
More than 15,000 refugees have fled to Nigeria amid Cameroonian military operations against the Anglophone separatists, the United Nations refugee agency and Nigerian government officials said earlier this month.
For a graphic on the Cameroon refugee crisis, click - http://tmsnrt.rs/2Djfjx5
(Additional reporting by Paul Carsten and Felix Onuah in Abuja; Writing by Joe Bavier; Editing by Janet Lawrence)