Japan and Saudi Arabia condemned "grave" human rights violations by Syria's regime which they said has lost its "legitimacy", in a joint statement on Wednesday after a meeting of top officials.
Japan's Prime Minister Shinzo Abe arrived Tuesday in the OPEC kingpin, where he met with Crown Prince and Defence Minister Salman bin Abdulaziz.
"Both sides condemned the continuation of grave violations of human rights by the Syrian authorities," said a joint Saudi-Japanese statement.
They also stressed that the "regime had lost its legitimacy."
Voicing support for the opposition Syrian National Coalition, both countries hoped the umbrella group would play a leading role in a political transition in the war-torn country.
They also "stressed their concerns for the rapidly deteriorating humanitarian situation in Syria," and pledged continued contributions to answer urgent needs, in coordination with international organisations.
Syria has been locked in a deadly conflict that began with a peaceful uprising against President Bashar al-Assad's rule before it descended into a full-scale war between his forces and armed opposition groups.
Saudi Arabia is among the Gulf states accused by Damascus of sending arms to the rebels.
More than 70,000 people have been killed since the uprising began in mid-March 2011.