The Latest: 2 US troops, 2 US civilians dead in Syria blast Two U.S. soldiers and two American citizens were among those killed Wednesday in a suicide bombing in northern Syria

BEIRUT -- The Latest on developments in Syria (all times local):

10:20 p.m.

Two U.S. soldiers and two American citizens were among those killed Wednesday in a suicide bombing in northern Syria.

U.S. Central Command says one of the civilians was employed by the Defense Department and the other was a contractor. The names of the American victims were being withheld until their families are notified.

The Islamic State claimed responsibility for the explosion.

The attack, which observers say killed at least 16 people, comes less than a month after President Donald Trump declared he was withdrawing U.S. forces from Syria, and that IS had been defeated. Three U.S. service members were injured in the bombing, which struck a busy marketplace in the strategic northeastern town of Manbij.

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7:25 p.m.

Turkish President Recep Tayyip Erdogan says that an explosion that killed American service members in Syria may have been an act aimed to deter the United States from withdrawing troops.

Erdogan said, however, that U.S. President Donald Trump appears to be determined to pull troops out and that he doesn't think the U.S. leader would step back from his decision.

The blast occurred during a routine patrol in the northern Syria town of Manbij.

"The attack in Manbij could be (aimed) to influence the decision to withdraw," Erdogan said: "Because I saw Trump's determination to withdraw, I believe that he will not take a step back in the face of the act of terror.

"If there is a step back, that that would amount to a victory for Daesh," he said in reference to the Islamic State group.

Erdogan spoke Wednesday during a joint news conference with visiting Croatian President Kolinda Grabar-Kitarovic.

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6:40 p.m.

Vice President Mike Pence is claiming that the Islamic State "caliphate has crumbled" and the militant network "has been defeated."

But his comments Wednesday in a speech at the State Department came shortly after the U.S. military said American service members were among those killed during an explosion during a routine patrol in Syria.

It's unknown how many U.S. troops were killed in the blast in the northern Syria town of Manbij.

Pence defended President Donald Trump's decision to withdraw the 2,000 U.S. troops from Syria. Critics say the pullout is premature.

He says the withdrawal will be "orderly and effective" and that the U.S. will stay in the region to make sure IS does not regroup.

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6:05 p.m.

The new U.N. special envoy for Syria says he has had "constructive" meetings with Syrian officials during his trip to the Arab country.

Geir Pedersen, the veteran Norwegian diplomat, spoke Wednesday, a day after he began his first visit to Syria since taking his new post earlier this month.

Pedersen took over from Staffan de Mistura, who stepped down for family reasons after four years and four months of peace efforts that led nowhere.

He told reporters: "We had constructive meetings and we agreed that we would continue to have close contact in the future. Absolutely."

Nearly half a million people have been killed in the nearly 8-year-old civil war in Syria and various U.N.-led peace efforts and indirect talks between the Syrian government and opposition in Geneva ended in failure.

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5:05 p.m.

The U.S. military says American service members have been killed during an explosion while conducting a routine patrol in Syria.

The military said in a tweet about Wednesday's blast in the northern Syrian town of Manbij: "We are still gathering information and will share additional details at a later time."

A Syrian war monitor, the Britain-based Syrian Observatory for Human Rights, reported earlier that at least two U.S. soldiers were killed in the suicide attack outside a restaurant in Manbij.

The Kurdish Hawar news agency, based in northern Syria, said three Americans were killed.

The blast killed a total of 16 people including nine civilians according to the Observatory.

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4:40 p.m.

The main Kurdish-led group backed by the United States in Syria says it will support efforts to establish a "safe zone" in northern Syria.

In a statement Wednesday, the Syrian Democratic Forces says: "We will offer all the support and assistance to set up the safe zone that is being discussed, in a way that guarantees the protection of all co-existing sects and ethnicities from annihilation." It called for international guarantees for this protection.

The statement came a day after Turkey's president said his country will establish a 20-mile- (32-kilometer-) wide "safe zone" in northern Syria, adding that Turkey would seek logistic and financial assistance from the United States and other allies to create the zone.

It reflects serious Kurdish concerns at being targeted by Turkey once U.S. troops pull out from Syria.

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1:45 p.m.

A Syrian war monitoring group and a local town council say an explosion has taken place near a patrol of the U.S.-led coalition in the northern town of Manbij and that there are casualties.

It wasn't immediately clear if the casualties include troops of the U.S.-led coalition.

The Britain-based Syrian Observatory for Human Rights and the Kurdish-led Manbij Military Council, which runs the town, say the blast occurred near a restaurant on Wednesday.

The Observatory says the explosion was likely set off by a suicide bomber. No further details were immediately available.

The attack comes as the U.S. has begun the process of withdrawing from Syria.