The UN-Arab League representative Lakhdar Brahimi's visit is part of international efforts to convene a peace conference in Geneva next month, but prospects for the talks remain unclear, with the Syrian opposition divided and due to vote next week on whether to take part.
Brahimi's tour comes as Saudi Arabia, a staunch backer of the opposition, in an unprecedented move on Friday rejected a seat on the UN Security Council in part to protest the world body's failure to act against the regime of President Bashar al-Assad.
The Saudi government said "allowing the ruling regime in Syria to kill and burn its people" with chemical weapons is "irrefutable evidence and proof of the inability of the Security Council to carry out its duties and responsibilities".
On the ground, the Syrian Observatory for Human Rights reported dozens of deaths in the northern province of Aleppo Friday, including 12 Kurds killed by regime shelling in the town of Tal-Aran, where nine people were killed on Thursday.
The town lies on a strategic route between Aleppo city and Sfeirah, a town under rebel control near a military base where the regime is believed to store some of its chemical arsenal.
Elsewhere in the province, the Observatory said at least 20 regime troops and seven rebels were killed after opposition forces attacked an air defence base southwest of Aleppo city.
The plight of civilians in the war-torn country prompted a strongly worded statement from the United States, calling on the Syrian regime to give access to humanitarian aid convoys, and warning against further massacres.
There were now "unprecedented reports of children dying of malnutrition-related causes in areas that are only a few miles from Bashar al-Assad's palace in Damascus," said State Department spokeswoman Jen Psaki on Friday. She added that "the regime's deliberate prevention of the delivery of lifesaving humanitarian supplies to thousands of civilians is unconscionable".
Also Friday the Red Cross in Syria released a video appeal for the immediate release of three kidnapped staff, warning if not, "it will affect negatively the aid we are trying to bring to the Syrian people".
With the regime and the increasingly divided rebels locked in an apparent stalemate, the international community has made a renewed push to convene a peace conference in Geneva.
Brahimi begins his travels on Saturday in Egypt, the first leg of a regional tour to prepare the ground for the conference.
In Geneva, spokeswoman Khawla Mattar said Brahimi would meet in Cairo with Egypt's foreign minister as well as the head of the Arab League. The full itinerary for the trip has not been finalised, she added, but stops in Syria and Damascus ally Iran are expected.
US Secretary of State John Kerry, who has also been pushing for the conference, will head to Europe next week for talks on Syria. Kerry and other envoys from the so-called London 11 -- the core group of the "Friends of Syria" -- will meet with the Syrian opposition in Britain on Tuesday to review progress towards convening the conference.
But the prospects for the talks remain dim, with the opposition divided on even the question of whether to attend.
The National Coalition, Syria's main opposition bloc, said it would hold internal discussions next week to decide whether to do so. The Syrian National Council, a key member of the Coalition, has already said it opposes the talks and threatened to quit if the umbrella group takes part.
The international community has been urging the rebels and the regime for months to participate in talks on a negotiated solution to the conflict, which has killed an estimated 115,000 people since March 2011.
But Assad's government says his departure from office will not be on the table, while the opposition insists he cannot remain in power.
The renewed push for talks, which were mooted as early as May, comes after a September deal under which Syria agreed to turn over its chemical arsenal for destruction.
Inspectors from the Organisation for the Prohibition of Chemical Weapons, which won this year's Nobel Peace Prize, said Friday they have visited 14 out of more than 20 sites in Syria.