AKIPRESS.COM - Islamic State militants have seized the last Syrian government-controlled border crossing between Syria and Iraq, a monitoring group says, reports BBC.

Government forces withdrew from the al-Tanf crossing in Homs as IS fighters advanced, the Syrian Observatory for Human Rights (SOHR) said.

The loss of al-Tanf to IS follows the group's takeover of the ancient city of Palmyra on Thursday.

The US says that fighting the militants will be a "difficult challenge".

Islamic State now controls "more than 95,000 sq km (36,679 sq miles)" of Syria, which is 50% of the country's entire territory, the SOHR said.

The militants dominate the provinces of Deir Ezzor and Raqqa and have a strong presence in Hasakeh, Aleppo, Homs and Hama.

However, correspondents say there are large areas under IS control in the east that are not very significant strategically.

On Thursday the United Nations said it had received reports that Syrian forces in Palmyra prevented civilians from leaving, ahead of its fall to Islamic State.

It said it was "deeply concerned" about the plight of those remaining in the area, amid reports of summary executions.

IS has also overrun the World Heritage site adjacent to the modern city, raising concerns about its future. The militants have previously demolished ancient sites that pre-date Islam.