Mexico and Canada are putting aside their differences and forming a more united front as they try to head off US President Donald Trump’s threat to impose steep tariffs on them as soon as next week. Since winning the election in November Trump has repeatedly threatened his country’s two largest trading partners with tariffs of 25 per cent on all exports to the US in retaliation for what he says are rising levels of illegal immigration and the trafficking of the opioid fentanyl into the country.

Active-duty military troops are set to begin arriving in El Paso, Texas, and San Diego on Thursday evening, marking the initial phase of deploying new forces to secure the southern border, according to defense officials.