Yasemin Vatansever and Yatunde Diya, both of north London, were arrested at Accra international airport on 2 July.

They denied the charge of attempting to smuggle more than 6kg (13lbs) of the drug on a BA flight to London.

The girls were found guilty by a Ghanaian court and could face up to three years in a juvenile detention facility when sentenced on 5 December.

The BBC's Will Ross in Accra said the girls will appeal against the verdict.

"They are very upset at the moment," said lawyer Sabine Zanker, of Fair Trials Abroad, after the 90-minute hearing in a closed juvenile court.

'Ruthlessly exploited'

"Their families are very deeply disappointed about the verdict."

She added: "These are two extremely vulnerable young girls whose naivety was ruthlessly exploited by the man who lured them to Ghana and led them to this terrible fate.

"They are together. It is a real blessing that they are together because it would be much harder if they were apart. They are very supportive of each other."

They had told the court they were set up, but the prosecution said they were involved from the start in a plot to smuggle drugs.

The girls have already spent nearly five months in custody after they were arrested with laptop bags containing cocaine.

Joint operation

Ms Zanker added that it was unlikely the girls would be able to serve their sentence in the UK as, at the moment, there is no transfer agreement between the two countries.

The girls were tried under Ghana's Juvenile Justice Act which meant their trial had to be completed within six months.

They were caught under a joint operation set up between the UK and Ghana, a year ago, to combat drug smuggling from the west African country.

So far "tens of millions of pounds of drugs" has been seized and stopped from reaching the UK, the HM Revenue and Customs (HMRC) said.