Sanaa has accused religious figures from Shi'ite power Iran of funding the rebels, though has stopped short of accusing the Tehran government, a traditional supporter of Shi'ite causes.
Iran denies any involvement but has encouraged Yemen to end the conflict centred on Saada province through dialogue.
A U.S. official said on Friday that Washington has no independent information that Iran is supporting Yemen's Shi'ite rebels, often termed Houthis after their leaders' family name.
But Ali Mohamed al-Anisi, chairman of Yemen's national security agency and head of the presidential office, said Sanaa has proof of Iran's involvement.
"There are indeed signs, proof of Iranian interference, but we say we can't elaborate on what these indications and their details are to the media," he said on the sidelines of a security conference in Bahrain.
Yemen said in October it had seized a ship carrying weapons destined for the Houthis and detained its Iranian crew. Iran said the report was a fabrication.
Anisi said the boat was Iranian and possibly linked to Eritrea.
"The last boat, an Iranian boat, to arrive at the port of Medi, near Malahidh region, which is also close to Saada — there are signs it came from Eritrea," he said. He gave no more details.
He also said al Qaeda was backing the rebels.
"Al Qaeda have a link to the Houthis," Anisi said, adding that a Saudi militant who Yemen handed over to Saudi Arabia had made comments of support for the Shi'ite rebels.
Al Qaeda is a Sunni Muslim group partly inspired by Saudi Arabia's puritanical Wahhabi school of Islam, which considers Shi'ism a deviant form of the faith.
The Houthis, who come from Yemen's Zaidi Shi'ite minority, accuse the government of veteran president Ali Abdullah Saleh of allowing Wahhabism influence in Yemen through his close ties to Saudi Arabia.
The United States and its ally Saudi Arabia, the world's largest oil exporter, fear the growing instability in Yemen could turn into a major security threat as the chaos allows al Qaeda to gain strength in the impoverished country.
As well as the northern rebellion, Saleh faces resurgent al Qaeda militancy and separatists complaining of marginalisation who want to reestablish south Yemen as a separate state.
The conflict in northern Yemen drew Saudi Arabia last month when the rebels seized some Saudi territory, prompting Riyadh to launch a military offensive against them. The rebels accuse Riyadh of backing Sanaa militarily since the war started.
(Writing by Andrew Hammond; editing by Michael Roddy)
