Ban said he was "gravely concerned" as the Security Council met behind closed doors to hear a report from his special envoy on the apparent bid to overthrow President Abdrabuh Mansur Hadi.
The UN chief urged "all sides to immediately cease all hostilities, exercise maximum restraint, and take the necessary steps to restore full authority to the legitimate government institutions."
UN envoy Jamal Benomar told the council that the Shiite militia known as the Huthis had launched a "masssive attack using heavy weapons" on the palace, a diplomat present at the closed meeting said.
The envoy, who briefed from Doha by video link, said he would travel to Sanaa immediately to try to help restore stability.
The Security Council meeting was requested by Britain following heavy clashes on Monday between the Huthis and the presidential guard in Sanaa.
Following a brief lull overnight, Huthi gunmen seized the palace on Tuesday and attacked Hadi's residence, with the president reportedly inside and meeting with visitors.
Benomar said Hadi was at his residence when fighting broke out on Monday but he could not provide more information on his fate, according to the diplomat
The envoy said the Huthis had convinced government armed units not to take part in the fighting, leaving only the presidential guard to fight.
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The 15-member council was expected to issue a statement following the emergency meeting to condemn the attack and apparent coup attempt.
British Ambassador Mark Lyall Grant told reporters the statement would call "on all spoilers to the political process to desist from their actions or face the wrath of the international community."
Benomar has been leading negotiations on forming a unity government in Yemen but faces resistance from the Huthis who have tightened their control over Sanaa since they overran the capital in September.
Ban also condemned the kidnapping by the Huthis on Saturday of Hadi's chief of staff, Ahmed Awad bin Mubarak, and called for his immediate release.
Hadi's government has been a key ally of the United States, allowing Washington to carry out repeated drone attacks on Al-Qaeda militants in its territory.
Yemen's branch of the jihadist network, Al-Qaeda in the Arabian Peninsula, is considered its most dangerous and claimed responsibility for this month's attack in Paris on French satirical weekly Charlie Hebdo that left 12 dead.
Yemen has been wracked by instability since an uprising forced leader Ali Abdullah Saleh from power in 2012.
The council in November imposed sanctions on Saleh and two allied Huthi commanders for threatening peace in the impoverished Arab country.
Saleh has been accused of backing the Huthis and a source in the presidential guard told AFP some Yemeni troops still loyal to the ex-leader had supported the militia in Monday's fighting.