WARSAW — NATO agreed Saturday to expand military patrols in the Mediterranean in a response to the threat posed by the Islamic State and the ongoing migration crisis involving people fleeing wars in Iraq, Syria, Libya, and other countries.

The patrols could include sea and air deployments, said Army General Curtis Scaparrotti, NATO’s top military commander and chief of the US European Command.

Leaders of the 28-nation military alliance said they would provide increased military support to countries in the Middle East and North Africa that are targets of Islamic extremism, including using NATO surveillance planes in the fight against the Islamic State.

NATO leaders also agreed to maintain a stable military presence in Afghanistan and to fund Afghan security forces through 2020.

‘‘We’re moving forward with the most significant reinforcement of our collective defense any time since the Cold War,’’ President Obama said at a news conference at the end of a NATO summit in Warsaw.

The White House has announced that Obama would cut his Europe trip short by one day in the wake of the massacre in Dallas. Obama headed to Spain on Saturday for meetings with Spanish leaders. He returns to Washington on Sunday and will visit Dallas early next week at the request of Mayor Mike Rawlings.

NATO Secretary-General Jens Stoltenberg said the alliance will start a training mission for Iraqi armed forces in Iraq, a country he called central in the fight against ISIS, the Associated Press reported.

NATO is also working to establish an intelligence center in Tunisia, a major recruiting ground for ISIS, and will shortly start providing support to Tunisian special operation forces.

‘‘Today we have taken decisions to strengthen our partners and to project stability beyond our borders,’’ Stoltenberg told reporters.

He said millions of people in Africa and the Middle East have been rendered ‘‘homeless and helpless’’ by radical organizations like ISIS and that the extremist groups are also to blame for organizing terrorist attacks in Europe and America.

Presently, the alliance works in the eastern Mediterranean and the Aegean Sea in support of a European Union-led mission on migrant operations, but that could be expanded to focus on areas near Libya and assisting the US-led effort campaign against the Islamic State in other ways, Scaparrotti said.

Scaparrotti said the new mission could include counterterrorism operations, maritime surveillance, and working with partner forces in the area.

Scaparrotti said he did not know yet whether the United States will have a role in the new maritime mission, but it could involve both US ships and aircraft.

Presently, the USNS Grapple, a salvage ship, is deployed in the Aegean Sea for the migrant mission.

The new mission emerged after NATO leaders at the summit firmed up support for deployments in Afghanistan in 2017 and met with Afghan President Ashraf Ghani.

US administration officials, speaking on the condition of anonymity to discuss internal deliberations, said they expect about 5,500 NATO troops will be there next year in addition to 8,400 US service members that Obama announced will deploy.

Obama’s decision deviated from a previous plan to have 5,500 US troops in Afghanistan in 2017.

The 8,400 troops will include about 6,700 devoted to the military advising mission known as Resolute Support and 1,700 devoted solely to counterterrorism operations through a separate mission known as Freedom’s Sentinel.

Scaparrotti said he agreed with the new plan and that it will allow the US military to continue training the Afghan air force and commandos in a fashion similar to what it does now.

It also will still provide some advising to conventional Afghan forces through expeditionary training teams that each focus on a specific region of the country, but a ‘‘little less than what it has been to this point,’’ the general said.

A senior administration official denied that deploying 8,400 US troops next year is a compromise between keeping the 9,800 there now and shrinking to 5,500 as previously planned.

Rather, it came after the top commander in Afghanistan, Army General John Nicholson, carried out a review and conferred with Defense Secretary Ashton Carter and other senior military leaders.

Stoltenberg said it’s too soon to say exactly how many troops individual allies will agree to keep in Afghanistan. But he said he believed that, based on commitments made Saturday, force levels will remain largely stable.