Riyadh, Saudi Arabia (CNN) President Barack Obama emerged from meetings with Gulf leaders Thursday proclaiming he'd pushed through lingering tensions with the region to reach agreements on battling ISIS and stabilizing the ever-volatile neighborhood.

But he also conceded that his nuclear deal with Iran remained a source of strain. Obama said the pact didn't reflect a shift in U.S. allegiances, however, citing longstanding efforts to bolster the security of Middle East allies.

"The fact of the matter is friendship and cooperation between the United States and Gulf countries has been consistent for decades," Obama said following a day of talks at the ornate Diriyah Palace in Riyadh. He cited ongoing efforts to battle ISIS and install a functioning government in Libya as examples of current areas of agreement.

But he acknowledged "tactical differences" in dealing with Iran, which the Sunni Gulf nations are carefully monitoring as Western sanctions are eased.

"We have to be effective in our defenses and hold Iran to account when it's acting in ways that are contrary to international rules and norms," Obama said, adding that it was also important to engage the moderate elements of Iran's government to produce deals like the nuclear accord.

Obama spent Thursday working to persuade other Gulf leaders to take a more muscular role in stabilizing their region.

He pressed the various kings, emirs and sultans of Saudi Arabia, the United Arab Emirates, Kuwait, Oman, Bahrain and Qatar to provide more support to war-torn Iraq as a U.S.-backed coalition takes back ground from ISIS. He also worked to convince leaders to provide more resources to opposition fighters in Syria, and to lend firmer backing to a political transition process in the civil war-torn country.

He said after his meetings that he shared the Gulf leaders worries' about the government of Iraqi Prime Minister Haider al-Abadi, citing "significant" disputes among the country's Shiite political blocs.

"I'm concerned. I think Prime Minister Abadi has been a good partner for us," Obama said. "Ultimately it's up to Iraqis to make decisions."

Saying he's secured commitments from the assembled leaders to step up assistance to Iraq, Obama said it was too soon to tell where those new resources would be used.

Thursday morning Obama met individually with the leaders of Kuwait and Qatar to make his case, the White House said, followed by a series of group meetings. But in both his bilateral talks and in the larger sessions, Obama faced the same skepticism that has clouded ties between Washington and Riyadh: fears over a resurgent Iran, doubts at Obama's Syria strategy and differences in fighting terror.

Three sessions

Obama's schedule at the Gulf Cooperation Council summit was broken into three sessions Thursday, with the first focused on stabilizing regional conflicts. U.S. officials said that discussion included Yemen, where a fragile ceasefire between the government and Iran-backed rebels hasn't stalled fighting; and Libya, where a power vacuum has led to an inflow of ISIS militants.

"I think there's broad agreement on where we're trying to go in the region," Obama's deputy national security adviser Ben Rhodes told reporters Thursday. "People would like to see stability restored to Yemen and a political transition in Syria away from (President Bashar al-) Assad, and people would like to see Iraq maintain its unity and increase its stability. On the core issues there's agreement on where we want to go."

But Rhodes acknowledged there have been "occasional tactical differences on what we are emphasizing at any point of time."

The President and the Gulf leaders also convened two other separate sessions, one focused on fighting terror and another on Iran , whose moves following the easing of Western sanctions are being closely monitored by its Arab Gulf neighbors.

Obama departed Riyadh soon after his meetings ended for a three-night stay in London.

Saudis' wary eye

Obama arrived for his brief visit to the Saudi kingdom Wednesday, looking to overcome a strain in ties between Riyadh and Washington.

Aside from fears over the Iran deal, the Saudis are anxiously eyeing Obama's decision on declassifying pages that could shed light on the country's hand in the September 11 terror attacks. They're also monitoring U.S. efforts to combat ISIS in Iraq and Syria with some degree of doubt.

Officials here also balked at Obama's suggestion in a recent magazine interview that the kingdom wasn't pulling its weight in global military efforts.

Emerging from a two-and-a-half hour meeting between Obama and Salman, U.S. officials described a productive session they claimed reduced some of the awkwardness that had seeped into the bilateral relationship. One official said Obama "really cleared the air" with Salman during their talks at the Erga Palace in Riyadh.

While Saudi officials have recently threatened to withdraw assets from the United States if pending legislation allowing families of September 11 victims to sue foreign governments, that topic did not arise during Obama's meeting with the monarch.

JUST WATCHED Can Obama smooth relations with Saudi Arabia? Replay More Videos ... MUST WATCH Can Obama smooth relations with Saudi Arabia? 05:37

U.S. to Gulf nations: Do more

In parallel meetings this week, U.S. Defense Secretary Ash Carter has pressed his Gulf nation counterparts to step up their assistance to Iraq, where a U.S.-backed government is still struggling to rebuild after years of war and invasion of certain regions by ISIS.

Carter said during a news conference he encouraged Sunni-majority Gulf nations to "do more ... not only militarily, as Saudi Arabia and the UAE have been doing -- and I really appreciate that -- but also politically and economically."

"Sunni support for multisectarian governance and reconstruction, particularly in Sunni areas of Iraq, will both be critical to ensuring that ISIL stays defeated," Carter said, using the administration's term for ISIS.

In particular, American officials have pressed Gulf nations to help rebuild areas of Iraq previously held by ISIS, including areas of Anbar province. Obama often touts successes on the ground in Iraq and Syria as evidence of a successful anti-ISIS campaign, but officials worry that retaken ground could be lost without an influx of resources.

In a meeting with Abu Dhabi Crown Prince Sheikh Mohammed bin Zayed Al Nahyan late Wednesday, Obama "reiterated the importance of stabilizing areas of Iraq liberated from ISIL," according to the White House.

The pair also discussed Libya and the fragile ceasefire in Yemen. U.S. officials hope that an end to fighting there will free up Gulf nation resources to go after ISIS more aggressively.

Regional conflicts

The GCC meetings are a follow-up to a summit convened at Camp David last year, which was meant to reassure U.S. allies amid final negotiations over the Iran nuclear deal. In both his talks with Salman and the Abu Dhabi crown prince, Obama sought to underscore the U.S. commitment to regional stability while encouraging a new relationship with Iran.

"This conflict between the GCC and particularly between Saudi Arabia and Iran, it fuels chaos, sectarianism, and instability in the region, all of which help ISIL and other terrorist groups," said Rob Malley, Obama's coordinator for Middle East policy, using a different term for ISIS. "It's clear who our allies and who our partners are. But if there could be a different relationship between the GCC and Iran, one that is less prone to fuel proxy wars. It's our conviction, and certainly the President's conviction, that that would be good for the region."