Over the next 10 days, Allen would travel to Britain, France, Saudi Arabia, Kuwait, Bahrain, Qatar, United Arab Emirates and Oman to meet with a wide range of government officials, regional partners, and multilateral institutions in support of international coalition efforts to degrade and defeat ISIL.
Allen is accompanied by Deputy Special Presidential Envoy Brett McGurk.
The White House has defended its decision to supply arms to the fighters in Kobani against ISIL.
"I can tell you that the President made clear why we consider it urgent and essential to resupply the fighters in Kobani who are in a desperate situation in their struggle to counter ISIL's assaults on the city," White House Deputy Press Secretary, Eric Schultz, said.
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Schultz said the US and Turkey have a shared interest in defeating ISIL, seeing a political transition in Syria, and bringing stability to Iraq.
The Pentagon said that the situation in Kobani is serious and thus the urgency to airdrop arms to local fighters who are giving a tough fight against ISIL.
These were provided by Kurdish authorities in Iraq and intended to enable continued resistance against ISIL's attempts to overtake Kobani, said Pentagon Spokesman Army Col. Steve Warren.
So far the US forces have conducted more than 135 airstrikes against ISIL in Kobani.