"I expect that all options are going to be on the table looking at this."
Feltman added that Washington's year-long policy of engagement with Syria was working.
'Excuse' to attack
Syria has firmly denied the Israeli claim, saying Israel might be looking for an excuse to attack.
Shimon Peres, the Israeli president, had openly accused Syria of providing high-grade weapons to Hezbollah, which he said could dramatically increase their ability to attack the Jewish state.
|Israel attacked Lebanon in retaliation against Hezbollah's rocket attacks [GALLO/GETTY]
Speaking on Wednesday, Feltman said he had received a "categorical denial" of any such missile transfer from Walid al-Moualem, the Syrian foreign minister.
Saad al-Hariri, the Lebanese prime minister, has also rejected the claims, saying Israel was concocting the allegations to threaten his country.
In 2006, Israel launched a full-scale war against Lebanon in response to an attack by Hezbollah on Israeli border towns in which they used rockets less sophisticated than Scuds.
The 34-day war killed 1,200 Lebanese, mostly civilians, and more than 160 Israelis, mainly soldiers, as the intensity of the conflict escalated.
Hezbollah was the only group that did not disarm after Lebanon's 1975-1990 civil war.
Syria has long played a dominant role in Lebanon but withdrew its last troops in 2005 after the assassination of Rafiq Hariri, the former Lebanese prime minister.
Ahmed Salkini, a spokesman for Syrian embassy in Washington, told Al Jazeera the reports of the alleged missile transfers were part of a disinformation campaign by Israel to divert the world's attention from its actions on the ground.
"They [Israel] are trying to create a parallel reality where everybody is distracted by these allegations while diverting attention from what's happening on the ground... evicting Palestinians, destroying their homes, expanding settlements."
Salkini said it also showed how Israel was evading any responsibility for building peace in the region, by pressing ahead with its occupation of Arab land.
"Syria is calling for a comprehensive and just peace in the region, where Israel withdraws from all occupied territories the UN and the international community has declared as being illegally occupied," he said.
"In return, Syria along with all Arab countries as seen in the Arab Peace Initiative have promised a normalisation of relations... so it is land for peace."