Libya had asked a Security Council committee for an exemption to an arms embargo to make the purchases from defense contractors in the Czech Republic, Serbia and Ukraine.
Spain asked that the request be put on hold as UN envoy Bernardino Leon held talks on forming a unity government that could spearhead the battle against the IS jihadists, diplomats said.
His request was supported by Britain, France, Chile, Lithuania, New Zealand and the United States in line with demands that reaching a power-sharing agreement be given priority.
Libya had asked UN approval for deliveries of eight helicopters, six fighter jets, four fighter-bombers, 150 tanks, 150 personnel carriers mounted with machine guns, 10,000 automatic grenade launchers, 1,000 sniper rifles along with ammunition and mortar shells.
Libya's Ambassador Ibrahim Dabbashi told the council that the weaponry would help the internationally-recognized government protect oil fields and monitor borders.
The request came less than two weeks after Libya asked the council to fully lift the arms embargo imposed in 2011 when the country descended into violence after the uprising against Moamer Kadhafi.
Diplomats told AFP that the request for the arms shipments was put on hold, but that no date was set for a decision at a later time.
A UN panel of experts wrote to the Security Council last week to express concern that arms shipments to Libya could fall into the wrong hands.
In a letter seen by AFP, they warned of "transfers of materiel -- particularly tanks, small arms, light weapons and related ammunition -- to non-state actors directly by the official end-users to militias supporting them or indirectly following fighting and loss of control over stockpiles."
Libya is awash in weapons and considered a major arms trafficking hub for North Africa, as powerful militias battle for control of key cities and the country's oil riches.
Members of Libya's rival parliament are due to meet in Morocco for a fresh round of UN-brokered talks while a dozen political leaders are to hold negotiations in Algeria .
At a meeting of its foreign ministers, the Cairo-based Arab League urged the UN Security Council to "lift the arms embargo on the Libyan government."
It also called on the international community to "stop the flow of weapons and armor through air and sea from reaching the terrorist groups and organizations."
The League vowed to offer full political and financial support to Libya's legitimate government.
The League will "supply the government with the required aid to allow it to protect the country's sovereignty, including its army... to be able to continue its mission to eradicate terrorism," a statement said.