Jihadists from the Islamic State of Iraq and al-Sham bolstered their presence Thursday in the Syrian town of Albu Kamal on the border with Iraq, a monitoring group said.

The Syrian Observatory for Human Rights said the move came a day after members in the town of Al-Qaeda’s franchise in Syria, Al-Nusra Front, pledged loyalty to ISIS, giving it control over both sides of the frontier.

ISIS, which aspires to create an Islamic state that straddles Iraq and Syria, has spearheaded a lightning jihadist offensive that has already captured swathes of territory north and west of Baghdad. […]