They were likely to meet Foreign Minister Walid Muallem later, a source close to the UN delegation told AFP on condition of anonymity.
Their visit came as opposition sources said Saudi Arabia had stepped up its weapons deliveries to rebels in readiness for a major offensive in Aleppo province, including on government-held areas of the northern metropolis.
It also came as opposition leader Ahmad Jarba met French President Francois Hollande in Paris as part of efforts to secure Western as well as Gulf Arab weapons.
The United Nations accepted an invitation from the Syrian government for the visit by the two envoys on July 11, with the limited brief of "completing the consultations on the modalities" of an inspection mission.
The United States has accused forces loyal to President Bashar al-Assad of making limited use of its chemical weapons stockpiles during the conflict, a finding backed by other Western governments.
Long-standing Assad ally Russia has accused the rebels of using chemical weapons.
Damascus has insisted any investigation should focus on the use of chemical weapons in the northern town of Khan al-Assal in March, which it and Russia blamed on the rebels.
The town was captured by the rebels on Monday, in what diplomats at the United Nations said was a blow to the mission's hopes of gaining access.
"If the government does not control Khan al-Assal then there is little chance they will let UN experts in," said one UN Security Council diplomat.
The United Nations has received 13 allegations of the use of chemical weapons in Syria.
UN chief Ban Ki-moon is "gravely concerned" by the allegations, UN envoy on the Middle East peace process Robert Serry told the Security Council on Tuesday.
The United States has previously said the use of chemical weapons in the Syrian conflict would constitute a "red line" that would warrant greater involvement.
In Aleppo province, where the front lines have moved little in recent months, an opposition source said key backer Saudi Arabia was providing weapons for a major offensive.
"Saudi Arabia has decided that Aleppo city and province must fall. Weapons and ammunition, including anti-tank weapons, are arriving every day," the source said.
The capture of Khan al-Assal marked the first step in the offensive, the source added.
New opposition chief Jarba and rebel Free Syrian Army leader General Selim Idriss met Hollande to push him to agree to supply arms as well as non-lethal supplies to the rebels.
Hollande after the talks reiterated French "political and humanitarian" support for the Syrian National Coalition, but without referring to military backing.
Speaking to reporters, he also expressed support for humanitarian aid corridors.
The International Committee of the Red Cross warned on Wednesday that thousands of Syrian civilians besieged by government and rebel forces alike were in desperate need of aid.
After France, Jarba will head to New York for meetings at the United Nations.
In mainly Kurdish Hasakeh province, in northeastern Syria, violence raged for an eighth consecutive day between Kurdish fighters and jihadists, leaving 19 people dead, the Syrian Observatory for Human Rights said.
In Daraa province, near the Jordan border, 31 people were killed in fighting around the town of Nawa on Tuesday, the Observatory said.
"The rebels control large parts of Nawa, after having seized 10 to 15 positions," its director, Rami Abdel Rahman, said.
Nationwide, at least 203 people were killed on Tuesday, among them 71 civilians, the Observatory said.