British Prime Minister David Cameron says his government is planning tough new laws to deal with homegrown jihadists fighting in Syria and Iraq. They could be refused reentry into the UK.

“We will shortly be introducing our own new counter-terrorism bill in the United Kingdom: new powers for the police at ports to seize passports, to stop suspects travelling and to stop British nationals returning to the UK, unless they do so on our terms, new rules to prevent airlines that don’t comply with our no-fly lists or our security screening measures from landing in the UK,” said Cameron addressing the Australian parliament in Canberra. He is in Australia for the G20 Summit.

For the UK and other countries whose nationals have left to wage jihad, the fear is that the return of radicalised, battle-hardened extremists could pose a threat on home soil.

Hundreds of Britons are thought to have joined militant groups like the self-styled Islamic State. Security analysts say foreign fighters in Iraq and Syria now number in the thousands.