The officials, Vijay Nambiar, a senior adviser to Annan, and Terje Roed-Larsen, the senior UN envoy on Syria-Lebanon issues, would speak to officials in both countries, UN spokesman Stephane Dujarric said on Wednesday.
The trip on Thursday, Dujarric said, was to help Annan prepare a report to the Security Council on its resolution adopted last Friday that called for an end to fighting and authorised an expanded UN force of up to 15,000 troops.
But asked if the two UN officials would meet Hezbollah leaders or go to Syria, Dujarric said their full programme had not been set.
Roed-Larsen, a Norwegian diplomat, on a previous Middle East mission with Nambiar last month, was refused entry to Syria. Damascus, diplomats said, had barred Roed-Larsen because of his reports on a 2004 Security Council resolution demanding that Syrian forces withdraw from Lebanon and militia, such as Hezbollah, disarm.
His reports, before the current crisis, have also cited weapons flowing to Hezbollah across the Syrian border.