Turkish soldiers stand guard as Syrian refugees wait for transportation after crossing into Turkey from the Syrian town of Tal Abyad, near Akcakale in Sanliurfa province, Turkey, June 10, 2015. REUTERS/Osman Orsal (Reuters) - Senior U.S. officials have urged Turkey to do more to stop jihadists crossing its border with Syria, and the two NATO allies appear divided on the role of Kurdish militias in fighting Islamic State.

Retired General John Allen, appointed by U.S. President Barack Obama to build a coalition against Islamic State, held talks in Ankara on Tuesday and Wednesday with his Turkish counterparts on joint efforts to fight the Islamist militants.

Turkey has been a reluctant partner in the coalition, arguing that Syrian President Bashar al-Assad also needs to be forced from power and fearing territorial gains by Kurdish militias will fuel separatist sentiment among its own Kurds.

Turkey has watched with concern as Syrian Kurdish PYD forces, backed by U.S.-led air strikes, have pushed back Islamic State militants from Syrian towns near the Turkish border.

"Turkey has certain conditions and is discussing them with the United States ... It's important for our allies to understand Turkey's sensitivities," Ahmet Berat Conkar, head of parliament's foreign affairs commission, told Reuters.

Protecting Turkmen Syrians, who have been displaced by fighting in northern Syria in recent weeks, and preventing a new wave of refugees to Turkey were among Ankara's priorities, he said.

Conkar, who was not at the talks, said Turkey would continue to consider the PYD a terrorist organisation as long as it maintained links with the Kurdistan Workers Party (PKK), a militant group which has fought an insurgency against the Turkish state for three decades.

That puts it at odds with Washington.

"The Kurds are acting, and because the Kurds are capable of acting, we are supporting them, and that is successful," U.S. Defence Secretary Ash Carter told the Senate Armed Services Committee in Washington on Tuesday.

He also suggested Allen's delegation was pushing Turkish authorities to step up border security to prevent fighters and supplies from reaching Islamic State.

Washington was trying to "get the Turks to up their game", Carter said.

"They're a NATO ally. They have a strong stake in things, in stability to their south. I believe they could do more along the border."

Turkey has faced criticism from some Western nations for failing to do more to stop foreign fighters crossing and joining Islamic State. It argues that domestic intelligence agencies in the West need to stop their nationals being radicalised and travelling to Turkey in the first place.

It has sent additional troops and military equipment to parts of its 900-km (560-mile) border with Syria in recent days as fighting in the north intensifies.

(Reporting by Ercan Gurses in Ankara and Phillip Stewart in Washington; writing by Nick Tattersall; editing by Andrew Roche)