Trump says military is 'waiting for' migrant caravan after warning of 'invasion' across US border

President's comments come as US military reportedly prepares to send 5,000 troops to region

Donald Trump has said the US military is "waiting for" a migrant caravan heading for America's southern border in a tweet warning of an "invasion" of the country.

"Many Gang Members and some very bad people are mixed into the Caravan heading to our Southern Border," the US president wrote, without providing any evidence for the claim.

"Please go back, you will not be admitted into the United States unless you go through the legal process. This is an invasion of our Country and our Military is waiting for you!"

His comments came the same day it emerged the US military is reportedly preparing to send up to 5,000 troops to the border in response to the caravan, despite the fact the number of migrants continuing their collective journey has decreased each day.

The migrants, many of whom are women and children escaping grinding poverty and violence in Central America, must still travel around 1,000 miles to reach the nearest US border crossing at McAllen, Texas.

The trip could be twice as long if the 4,000 or so migrants head for the Tijuana-San Diego frontier, as another caravan did earlier this year. Only about 200 in that group made it to the border.

In addition to the military, Border Patrol officials are warning of self-appointed militia groups who plan to head to the Mexico border in a bid to challenge the caravan.

The activists, who are raising money for their plan, are planning to arm themselves with guns and bulletproof vests in an effort to secure America’s border.

Despite unverified claims by Mr Trump that the caravan features "criminals and unknown Middle Easterners", most escaping Guatemala, Honduras, and El Salvador are fleeing gang violence and rampant poverty.

Travelling by foot, trucks, and rivers in search of work or asylum in Mexico or the US, they appear undeterred at the prospect of family separation or detention, which is part of Mr Trump's "zero tolerance" stance on immigration.

But their journey is a central issue for many Republicans in midterm election campaigns, and increasingly an obsession for the US president, who is attempting to blame Democrats for the issue.

“Every time you see a Caravan, or people illegally coming, or attempting to come, into our Country illegally, think of and blame the Democrats for not giving us the votes to change our pathetic Immigration Laws!” Mr Trump tweeted last week.