BRUSSELS - The United States is renewing pressure on its European NATO allies to establish a long-term train-and-advise mission in Iraq, diplomats said, reviving a divisive issue for an alliance wary after a decade in Afghanistan.US Secretary of Defense Jim Mattis sent a letter to NATO headquarters in January calling for a formal NATO mission to Iraq with a semi-permanent or permanent command to train Iraqi forces, according to five senior NATO diplomats.After a three-year war with Islamic State, Washington wants to ensure the militants do not re-emerge. While NATO does have trainers in Iraq already, they number less than 20. NATO defense ministers are expected to discuss the US request in Brussels next week, with a possible decision at a summit in July.In his letter, Mattis left many details open but suggested developing military academies and a military doctrine for the Iraqi defense ministry, diplomats said. Other ideas cited by diplomats include bomb disposal training, maintenance of Soviet-era vehicles and medical training."The United States is pushing hard for a NATO role in Iraq, not in a combat role, but for a long-term assignment," said one senior NATO diplomat on condition of anonymity."This looks suspiciously like another Afghanistan," the diplomat said, referring to the long-running conflict where NATO is funding and training Afghan forces. "Few allies want that."Pentagon spokesman Johnny Michael declined to discuss whether Mattis had sent a letter to NATO but said: "The administration continues to look for ways allies can do more to counter terrorist organizations."A NATO official said that the alliance is "looking into how we can step-up our training efforts."NATO defense chiefs will provide ministers with a range of options for an Iraq mission, while NATO Secretary-General Jens Stoltenberg has discussed the issue with Prime Minister Haider al-Abadi, who supports a mission, diplomats said.The US push is also part of President Donald Trump's demand that the Western alliance go beyond its core task of defending its territory and help stem Islamic militancy.Trump scolded allies last May at a summit in Brussels, warning of more attacks in Europe if NATO did not do more to stop militants. Even his predecessor Barack Obama sought a greater NATO role in the Middle East.Then, US officials had raised the possibility of NATO taking over the running of the US-led coalition against Islamic State, as it did of the US-led mission in Afghanistan in 2003.The United States sees NATO's long experience in Afghanistan as putting it in an ideal position to help build up Iraqi forces after recapturing territory taken by Islamic State. The United States has more than 5,000 troops in Iraq.But European allies fear being pulled into another open-ended foreign assignment that is costly, unpopular at home and potentially dangerous.In a gesture to Trump, the 29-nation alliance agreed last year to join the coalition. However, France and Germany insisted that the decision was mainly symbolic.IRAQ ELECTION, LETTERThe size of any potential NATO mission has not been debated, but the diplomats said they would need to be substantially more than the current team to mollify Trump. They could involve regional training centers outside Baghdad."This is an area where we could demonstrate relevance," a second diplomat said, noting that allies were well aware of Trump's campaign criticism in 2016 that NATO was "obsolete" because it did not do more to combat militants.Creating a formal NATO mission would mean greater funding, so-called force generation to drum-up troops and a structure to keep them in the field for longer.Difficult issues include whether military trainers would require protection and who would provide it.Iraq would need to formally request the NATO mission, diplomats said. That would likely rely on Abadi winning re-election in May, as rival candidates backed by Iran are hostile to US troops remaining in the country.But the pressure is also greater because NATO has not yet been able to follow up on a similar train-and-advise request from Libya's U.N.-backed government in Tripoli, diplomats said, because the country is still controlled by rival factions.