Brussels - US Secretary of State Rex Tillerson said on Wednesday he expected Nato to overcome reservations and join the US-led anti-Islamic State coalition at a summit with President Donald Trump.Trump meets Nato leaders in Brussels on Thursday to press them to do much more to combat ISIS, with the deadly bomb attack in Manchester claimed by the group set to be high on the agenda."Nato joining the ISIS coalition, we do think that would be a really important step for them to take," Tillerson told reporters travelling with Trump."I think [Nato chief] Secretary Stoltenberg feels that would be an important step for them to take. There are a couple of countries that are still thinking it over," Tillerson added."I've had meetings actually with one of those. I think they're going to support Nato joining and becoming a member of the ISIS fight."All 28 Nato allies have joined the coalition as individual countries, while Nato has provided AWACS surveillance planes to support anti-ISIS operations in Syria and Iraq, along with limited training missions.But it baulks at any combat role and some allies, including France, Germany and Italy according to diplomatic sources, are reluctant for Nato to get more involved for fear of being dragged into a ground war and risking its standing with Arab powers.They are also concerned Nato could end up taking over control of the whole operation in Iraq when it remains bogged down in Afghanistan.'Brutal' attackEarlier on Wednesday, Stoltenberg said he believed the "brutal" Manchester attack showed the alliance must agree to do more."Many allies would like to see Nato as a full member of the coalition... because it sends a strong message of unity," he said."Especially in light of the attack in Manchester, I think it is important to send this message of unity against terrorism."Trump will also urge the allies to increase defence spending to the target of two percent of annual Gross Domestic Product they agreed in 2014.In return, the allies hope the president will unequivocally state his support for NATO's core Article 5 collective defence commitment.Asked about this issue, Tillerson said: "Of course we support Article 5. The only time Article 5 has been invoked was in the 9/11" attacks on the United States.But he refused to be drawn on what Trump might say."He is still working on final remarks so I don't want to tell you exactly what is going to be in the speech," he said.