The Lebanese news agency said the Lebanese man, who works as a driver with ride-hailing giant Uber, had confessed to killing the young woman, who was employed at the UK embassy in Beirut.
Dykes was last seen alive at a party in Gemmayzeh, a Beirut neighbourhood popular with foreign residents, on Friday night and left in the suspect's car.
"He picked her up in Gemmayzeh on Friday night, took her to Achrafieh then to the Metn highway and tried to rape her," the news agency said, referring to an expressway north of Beirut.
Her body was found dumped on the roadside there early the following evening.
A senior security official had told AFP that strangulation was the likely cause of death and added that Dykes was found with string tied around her neck.
The Lebanese news agency said the suspect was tracked down thanks to security cameras and confessed to killing Dykes after she resisted when he sexually assaulted her, it said.
A senior official in the judiciary said that she had booked her vehicle using the Uber app, whose driver identification and rating system is seen by many, especially women, as offering better safety guarantees than when hailing a cab off the street in Lebanon.
Such crime is rare in the Lebanese capital, a city which is considered generally safe, including for tourists and foreign residents. A senior official had stressed that the murder was "not politically motivated".
A picture of the young woman, who worked at the British government's Department for International Development (DFID), was on the front pages of many UK papers Monday.
The British ambassador in Beirut, Hugo Shorter, expressed his grief in a statement and messages of support for her family and colleagues poured in from Beirut's shell-shocked diplomatic and aid community.
"We are devastated by the loss of our beloved Rebecca. We are doing all we can to understand what happened," the family said in a statement passed on by the Foreign Office.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)
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