UNITED NATIONS - Secretary-General Ban Ki-moon said Monday that the Lebanese government should ratify an agreement with the United Nations to establish an international tribunal to prosecute the suspected killers of former Lebanese Prime Minister Rafik Hariri.

Lebanon's current prime minister, Fuad Saniora, sent a signed copy of the agreement to the United Nations last week, U.N. deputy spokeswoman Marie Okabe said. The agreement must now be signed by the United Nations and returned to Lebanon for ratification.

"We are now taking necessary steps," Ban told reporters. "We hope that once the United Nations will sign this document, the Lebanese government should take necessary measures to ratify this in accordance with their constitutional procedures."

One stumbling block is that Nabih Berri, the pro-Syrian speaker of Parliament, has refused to put the tribunal agreement to members.

Hariri was killed with 22 others in a suicide truck bombing in Beirut in February 2005. The assassination sparked huge protests against Syria, which was widely seen as culpable. Syria denied involvement, but was forced to withdraw its troops from Lebanon, ending a 29-year presence.

A U.N. investigation into the assassination is still under way. The first U.N. chief investigator, Germany's Detlev Mehlis, said the killing's complexity suggested the Syrian and Lebanese intelligence services played a role in Hariri's assassination. Four Lebanese generals, top pro-Syrian security chiefs, have been under arrest for 16 months, accused of involvement in Hariri's murder.

Pro-Syrian Hezbollah militants, emboldened by their survival of Israel's bombardment during last summer's 34-day war, have been seeking to strengthen their political standing in the Cabinet led by Saniora, who is anti-Syrian.

The Hezbollah-led opposition has staged two months of demonstrations and sit-ins in a bid to topple Saniora to make way for a Cabinet in which Hezbollah and its allies would have a veto power on government decisions — including the tribunal.

Saniora, who is backed by a slim parliamentary majority and many foreign states such as France and the United States, has refused to step down. (AP)