Stefanos Stefanou, a government spokesman, said: "The president of the republic considered it appropriate to return to Cyprus to monitor and handle the situation on the ground."
Government officials said Turkish Cypriot police had breached an agreement by entering the 70m stretch of UN-controlled buffer zone that divides the city.
Kypros Chrysostomides, Cyprus' justice minister, said: "The agreement to open Ledra Street was made on clear terms... Unfortunately these terms were not respected and as a result there was a decision to close the road."
He said the crossing was reopened on assurances that Turkish Cypriot police would not re-enter the buffer zone, but warned that Ledra would again be shut down if more violations occurred.
Jose Luis Diaz, a UN peacekeeping force spokesman, said the UN had received assurances enabling it to "ensure the smooth functioning of the crossing point. But [that it would] take good will and cooperation on all sides".
Cypriots from both sides of the divide continued to cross Ledra Street on Friday, despite the earlier disruption.
Greek Cypriot police said 260 Greek Cypriots and as many Turkish Cypriots had crossed Ledra from midnight to noon on Friday.
The previous day nearly 1,200 Turkish Cypriots crossed southwards.
The Ledra Street opening has been hailed as a significant milestone in efforts to reunify Cyprus, split along ethnic lines in 1974, when Turkey invaded in response to a short-lived coup by supporters of the uniting island with Greece.
Christofias and Mehmet Ali Talat, the Turkish Cypriot leader, are set to begin reunification talks in June after a three-month preparation period.
Both have said they would seek a deal to reunify the island "as soon as possible".
Christofias was in London for a "progressive summit" by Gordon Brown, the British prime minister, a weekend of talks with more than a dozen world leaders that will focus on issues such as climate change, the economy and global poverty.