MEXICO CITY • The Trump administration calls the visit a step towards mutual understanding and a way to move the relationship forward.

But as US Secretary of State Rex Tillerson arrived in Mexico on Wednesday, twin threats hung over the frayed relationship between the two nations: President Donald Trump's new orders to round up and deport immigrants who are in the United States illegally and a separate effort to take a hard look at aid to Mexico, possibly using it to pay for a wall on the border between the two countries instead.

By today, US officials are required to finish calculating all the money that their country provides to Mexico - a task that Mr Trump first demanded in the executive order he signed last month directing the construction of a border wall.

The Trump administration has not said why it ordered the review.

But its inclusion in the executive order mandating that a wall be built suggests that Mr Trump has linked the two issues - and may be looking for more leverage in negotiations with Mexico.

The timing of the review adds to the deep tensions between the countries.

Mr Tillerson, the top US official to visit Mexico since Mr Trump's inauguration, arrived with Secretary of Homeland Security John Kelly only a day after the Trump administration released documents ordering a crackdown on immigration.

Mexican newspapers have described the deportation policies in apocalyptic terms, saying in some cases that they represented "war" on the millions of Mexicans who are in the US.

Mexican Foreign Minister Luis Videgaray said on Wednesday that the package of immigration directives is "something that, without doubt, worries all of us Mexicans" and will be "the first point on the agenda" when he meets his US counterpart.

The review of US aid is likely to highlight the sum of about US$1 billion (S$1.4 billion) that has been allocated but not yet spent under the Merida Initiative.

The bilateral partnership, begun in 2007, focuses on fighting organised crime, re-engineering the judicial system, modernising the border and strengthening civil society groups.

Since the initiative was signed, the US Congress has appropriated more than US$2.8 billion for those programmes.

At least US$1.6 billion has been delivered to Mexico, according to a report in January by the Congressional Research Service.

NYTIMES