He said they discussed regional security challenges both countries face - from terrorism to Iran's nuclear ambitions.
"As part of our steadfast support to Israel, the US continues to provide a robust annual military assistance package," Gates said.
"We are contributing both financial and technical assistance to strengthen Israel's defence against the growing threat posed by rockets and missiles, and we will continue to ensure that Israel has the most advanced weapons for its national defence."
But Gates cautioned that achieving long-term security for Israel "depends on a sustainable comprehensive" Middle East peace, a goal he said was important for regional stability.
For his part, Barak said the meeting touched on strategic and security issues, including the challenges and threats to the Middle East security and stability.
"The US and Israel have a long history of very close relationship based on common values, friendship and co-operation ... and we highly appreciate the commitment of the US to the security of Israel to keep its qualitative military edge," he said.
The talks were held a day after Mitchell met Barak in Tel Aviv and reaffirmed Washington's friendship with Israel.
Mitchell said: "Our discussions cover a wide range of issues, all of which are intended to help promote ... a desire for a comprehensive peace in the Middle East.
"That includes Israel and Palestine, Israel and Syria, Israel and Lebanon, and normal relations with all countries in the regions."
Al Jazeera's Mike Hanna, reporting from Jerusalem, said the flurry of meetings illustrated the change in Washington's approach to the peace process.
"The US is suddenly engaging in a diplomatic process that involves several things happening at the same time - unprecedented in terms of any peacemaking efforts within the region," he said.
"Instead of taking each thing point by point, the Obama administration appears to be addressing all of them simultaneously. It may be a gamble on one hand, but it is certainly something that is happening regardless of what happens."
The US has already signalled to Israel that it does not agree with construction activities in the east of Jerusalem, "something that was not brought up publicly between the US administration and Israel before", Hanna said.
"This sends a signal that it [the US] may question Israeli's authority over the whole of Jerusalem rather than the west of it."
Before travelling to Cairo, Egypt,
"Whether this effort will succeed or not does not depend on Syria, it does not [even] depend on America, it depends on Israel. We'll see if Israel will go on board"
George Jabbour, former Syrian member of parliament
Mitchell met Bashar al-Assad, the Syrian president, on his second visit to the country in as many months.
Damascus' support for Hamas, the de facto government in the Gaza Strip, and its relations with Iran, could make it key to US efforts to kick-start the peace process.
In a statement released after his meeting with al-Assad, Mitchell said he had communicated Obama's intention "to facilitate a truly comprehensive Arab-Israeli peace".
Relations between the US and Syria were strained under the administration of George Bush, the previous US president, but have begun to improve under Obama.
George Jabbour, a former Syrian member of parliament, said Mitchell's visit was proof that the US had become more serious about achieving peace in the region.
"The policy of Obama in the Middle East is different than the policy of George Bush," Jabbour told Al Jazeera.
"Whether this effort will succeed or not does not depend on Syria, it does not [even] depend on America, it depends on Israel. We'll see if Israel will go on board."
The round of US diplomacy with Israel comes amid tensions between the two allies, both over Iran and the Obama administration's firmer line on Israeli settlement building.
|Netanyahu is due to hold separate meetings with all three US officials [AFP]
A rare public row has erupted between Israel and the US as Washington tries to get Israel to freeze construction in all its West Bank settlements.
Binyamin Netanyahu, Israel's prime minister, said there were "naturally" differences of opinion between Israel and the US, but that the sides were "trying to reach an understanding".
Netanyahu is due to hold separate meetings with all three US officials.
Herb Keinon, the diplomatic correspondent for the Jerusalem Post newspaper, told Al Jazeera that the two sides are getting close to some kind of agreement on a suspension of settlement activity, but only in the West Bank.
"When Israel talks about a settlement moratorium, they're talking about a settlement moratorium in the West bank and not in East Jerusalem," he said.
"There is a big Israeli consensus that Jerusalem should not be lumped together with any agreement that might be reached about freezing construction in the settlements."
In East Jerusalem on Sunday, Israelis working on a property in the Arab neighbourhood of Sheikh Jarrah clashed with Jewish and Arab opponents, the Associated Press news agency reported, citing police.
Police said the Israelis working on the house had court-approved documents proving their ownership, but Palestinians said the empty building was the property of an Arab.