NAIROBI, March 20 (Reuters) - Rwanda's economy should grow by 7.6 percent this year from an estimated 7.7 percent in 2012, but lower aid disbursements and a tough global economic environment could erode this, the International Monetary Fund said.

Donors froze aid worth $240 million in the second half of 2012 - roughly 11 percent of the country's budget, the government said in December. The aid was suspended over Rwanda's alleged support for rebels in the Democratic Republic of Congo, an accusation Rwanda has repeatedly rejected.

"Growth is expected to be sustained at 7.6 percent in 2013, driven by an expansion in services and construction, and to stabilize at around 7 percent over the medium term," IMF said in a statement late on Tuesday.

"Risks to the outlook arise mainly from possible cutbacks in aid and a more challenging global environment. Staff estimates indicate that a prolonged delay in the delivery of budget support could lower growth in 2013 by 1.5 percentage points and possibly more, depending on the magnitude of second round effects."

Rwanda's central bank said in February it expected economic growth of 7.1 percent this year, from a previous forecast of 8 percent, while in December the then Finance Minister John Rwangombwa said economic growth could slow to as low as 6 percent this year as a result of the aid freeze.

The IMF said it expected inflation to converge towards the government's medium term target of 5 percent. Urban inflation slowed to 4.79 percent in February from 5.67 percent a month earlier.