Media playback is unsupported on your device Media caption Increased border security between the US and Mexico has made life for nearby residents difficult

The sharp decline in illegal immigration to the US during the long economic downturn has ended, researchers have estimated.

The number of immigrants in the US illegally edged up to 11.7 million in 2012 from 11.3 million in 2009, the Pew Research Center found.

The number of illegal immigrants had declined over several years from a high of 12.2 million in 2007.

The recent growth is largely driven by immigrants from outside of Mexico.

"As a whole, with the recession ending, the decrease in illegal immigration has stopped," said Jeffrey Passel, a senior demographer at Pew.

While the change is within the margin of error, evidence including increased apprehensions of migrants at the US border leads Pew researchers to speculate in a new report that illegal immigration is again rising.

Slack job market

Image caption Many new immigrants come through Mexico but are from further south

A more precise measure from the US Census Bureau is expected later this year.

Analysts said it was unclear if the number of unauthorised immigrants would rebound to the 2007 high, in part because long-term shifts in Mexico's economy were discouraging emigration.

"Labour demand in the US is still slack and wages are eroding, whereas there are jobs in Mexico and wages are slowly rising as labour force growth there decelerates," Douglas Massey, a professor of sociology and public affairs at Princeton University, told the Associated Press.

In addition, Mexico's labour force is aging, making workers less inclined to undertake the arduous journey across the US border, analysts say.

Immigrants from Mexico now make up 52% of illegal immigrants in the US, down from 57% in 2007, Pew estimated.

Meanwhile, illegal immigration from countries other than Mexico rose to a record 5.65 million in 2012, although that figure is preliminary.

A comprehensive immigration reform bill that would grant legal status to some of the illegal immigrants in the US has been stalled in the US House of Representatives since passing in the US Senate in June, in large part amid opposition from conservative Republicans who hold significant sway in the chamber.

In the meantime, President Barack Obama has used his executive authority to grant provisional legal status to some undocumented immigrants brought to the US as children.