Two Canadians, a Norwegian and a Filipina held captive for seven months in the southern Philippines could be beheaded on Monday by an Islamic rebel group that operates a ruthless kidnapping and piracy enterprise.

The Abu Sayyaf faction, which pledged allegiance first to al-Qaeda and now Islamic State of Iraq and the Levant (Isil), has set a deadline of 3pm for ransoms of £4.5 million to be paid for the three Westerners.

In videos chillingly reminiscent of those that have emerged from Syria, the three haggard-looking men plead with their families and governments to pay the money.

One captor presses a machete to their necks, while other armed men stand behind them carrying assault weapons and the distinctive black flag of Isil.

The shocking images and looming deadline have focused fears that Islamic extremists are carving out a safe haven for terrorists to use as a base to strike targets across South East Asia.

Abu Sayyaf splinter groups have also seized 18 Indonesian and Malaysian sailors in raids on coal tugboats in the past month, as they intensify their attacks in some of the world’s busiest waterways.

The surge in piracy prompted Indonesia’s security chief to warn that the trading route – part of major shipping arteries carrying $40 billion of cargo a year – could “become a new Somalia”.