US Secretary of State Mike Pompeo has defended Donald Trump's withdrawal of troops in Syria, saying the president did not give Turkey the "green light" to invade the country.

Speaking to PBS Newshour, Mr Pompeo said that during the phone call with Turkish President Recep Tayyip Erdogan "it became very clear that there were American soldiers that were going to be at risk and the president made a decision to put them in a place where they were out of harm's way".

He also added that he feels that Turkey has a "legitimate security concern" and waved off claims from Republican Senator Lindsay Graham that the attack could lead to a reemergence of IS.

The land assault in Turkey, alongside the Syrian National Army, came as US forces began withdrawing from the region on Sunday.

President Recep Tayyip Erdogan announced the start of the campaign, which followed Donald Trump's decision on Sunday to alter US policy.


Mr Erdogan has since said Turkish forces have killed 109 militants.

As the start of the operation was announced, TV reports in Turkey reported airstrikes in the towns of Ras al-Ayn and Tal Abyad.

Mustafa Bali, a spokesman for the US-backed Kurdish-led Syrian Democratic Forces (SDF), said Turkish warplanes were targeting "civilian areas" in northern Syria, causing "a huge panic" in the region.

Other reports suggested mortar shells had been fired into Turkey from the Syrian side of the border.

There has been no independent confirmation of these claims.

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NATO's secretary general has urged Turkey not to "further destabilise the region".

Jens Stoltenberg said Turkey "has legitimate security concerns" having suffered "horrendous terrorist attacks" and hosting thousands of refugees, but that it should act with "restraint" and any action should be "proportionate".

And France, Britain and Germany are preparing a joint statement to condemn the offensive while the UN Security Council will meet on Thursday.

Image: Turkey has proposed a safe zone, but the Kurdish-led Syrian Defence Force believe it will turn into a crisis zone

The Syrian Kurdish forces were long-time US allies in the fight against the so-called Islamic State group.

But expectations of an invasion increased after Mr Trump's announcement on Sunday, although he also threatened to "totally destroy and obliterate" Turkey's economy if the Turkish push into Syria went too far.

Mr Trump's move has drawn criticism from both Republicans and Democrats at home as well as allies including France and Britain.

Senators Chris Van Hollen (Democrat) and Lindsey Graham (Republican) have launched a bipartisan bill that would punish Turkey for its invasion of northern Syria.

The lawmakers said they expect wide support from both parties.

Sen Graham, normally a staunch Trump ally, said on Twitter: "While the administration refuses to act against Turkey, I expect strong bipartisan support.

Image: Streams of Turkish army vehicles arrived at the border on Tuesday

"Most members of Congress believe it would be wrong to abandon the Kurds who have been strong allies against ISIS."

However, Mr Trump defended it saying he is focused on the "BIG PICTURE" that does not include American involvement in "stupid endless wars" in the Middle East.

"Fighting between various groups that has been going on for hundreds of years. USA should never have been in Middle East," Mr Trump said in a series of tweets.

"The stupid endless wars, for us, are ending!"

Despite this, Mr Trump has said the US "does not endorse" Turkey's assault on Syria, and called the operation "a bad idea".

Turkey has been massing troops for days along its border and vowed it would go ahead with the military operation and not bow to the US threat.