From Jeddah, where he will meet senior Saudi leaders, Kerry will fly on Monday to Vienna where he will co-host international meetings on the two conflicts.
Then on Wednesday, he will fly on to Brussels for the NATO foreign ministers' meeting and talks on the full range of challenges facing the Western allies.
Kerry's spokesman John Kirby said the secretary of state and Italian Foreign Minister Paolo Gentiloni would jointly host the Libya crisis meeting.
Libya's new UN-backed government has been set up to unite the fractured country and fight the Islamic State group, but it is still a work in progress.
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Officials say the fledgling regime is drawing up a list of requests for Western partners to assist its forces with arms, training and intelligence.
After the Libya meeting, Kerry and Russian Foreign Minister Sergei Lavrov will lead a meeting of the 17-nation International Syria Support Group.
Kirby said the goal was to "ensure humanitarian access throughout the country, and to expedite a negotiated political transition in Syria."
Officials hope next week's meeting will inject new life into the peace process and -- if the ceasefire holds -- secure talks on forming a unity government.
And, with Russia and France, Kerry will also co-host a meeting on the Nagorny-Karabakh conflict with the rival Armenian and Azerbaijani presidents.