Dr. Abu Akram, who operates a makeshift hospital at Mua'adamiyat al-Sham, Syria, said the arrival of 12 inspectors was delayed by gunfire for 4 hours, and their departure, ordered by the Syrian regime, came 90 minutes after their arrival.
Akram said the inspectors, some of whom were doctors, included Canadians, Egyptians and Sudanese, and arrived in bullet-riddled vehicles.
The inspectors spoke with more than 20 victims of the suspected chemical weapons attack and the hospital took urine, blood and hair samples, documenting the victims' stories by videotape, the British newspaper The Guardian said.
They then visited the site of a suspected chemical rocket strike, took soil samples and several domesticated animals but did not take parts of the rocket or exhume any bodies of those who died, the newspaper said.
The team's work was delayed after their convoy was hit by sniper fire. Though the lead vehicle was destroyed, the team, led by Swedish scientist Ake Sellstrom, was unharmed. U.S. Secretary-General Ban Ki-moon said the U.N. will register a "strong complaint" with the Syrian government and opposition authorities about an attack "so the safety ... of the investigation team will be secured."
"What I am told is that despite the very difficult circumstances, our team replaced their car and returned to the suburbs of Damascus to carry out their investigation," he said.
"Anyone who can claim that an attack of this staggering scale ... was staged ... needs to check their conscience," Kerry said.
Syrian President Bashar Assad has denied troops loyal to him used chemical weapons and threatened dire consequences should his country be subjected to an airstrike.
"The area of the claimed attack is in contiguity with the Syrian Army positions, so how is it possible that any country would use chemical weapons in an area where its own forces are located?" he asked in an interview with Russian newspaper Izvestia.
Russia, one of a handful of allies to Syria, has accused rebels of staging the attack.
CNN reported there was an explosion near the site the inspectors planned to visit. Some witnesses said it was caused by incoming ordnance.
U.S. Defense Secretary Chuck Hagel said U.S. forces were "prepared to exercise whatever option" Obama ordered.
British Foreign Secretary William Hague would not discount bombing regime targets inside Syria soon, warning a diplomatic effort to resolve the crisis hasn't borne fruit.
William Hague also insisted Britain, the United States and France were united to act against Assad, The Daily Telegraph reported Monday.
Iran predicted "harsh consequences" if the United States intervened against the Iranian ally.
Israeli President Shimon Peres called for an international effort to "take out" Syrian chemical weapons.