Some 120 Guinea-Bissauan special forces have crossed into neighbouring Guinea where President Lansana Conte is facing an unprecedented popular uprising, a senior Bissau army officer said on Monday.

“The troops were based at the town of Gabu in eastern Guinea-Bissau and crossed into Guinea Conakry at the town of Buruntuma to support the army” on Sunday, the officer said.

Since 10 January the border between the two countries has been closed, according to authorities in Guinea-Bissau. Witnesses say the army and police in Guinea have killed at least 30 people in the past two weeks as protestors throughout the country have taken to the streets to demand the resignation of the country’s 72-year-old President Conte.

The Guinea-Bissau soldiers form part of an elite force called the Aguentas, meaning "survivors" in Portuguese. They received training in the Guinean capital, Conakry, in 1998 before returning to Bissau to help support Guinea-Bissau’s President Joao Bernardo "Nino" Vieira during a military uprising against him, military analysts in Bissau said.

The leaders of Guinea and Guinea-Bissau signed a military cooperation agreement in 1996, the same year as a brief uprising by the national army in Conakry. Conte is believed to have fled to Bissau at the time.

“Vieira is helping Lansana as Lansana helped him in 1996 and 1998,” a diplomatic source in Bissau said.

During the military revolt against Vieira in 1998, Conte sent Guinean troops to support him. The following year Vieira fled into exile after being overthrown by a military junta. He returned to Guinea-Bissau in 2005, and was elected president in elections deemed free, fair and transparent by European Union observers.