BERLIN (Reuters) - Demand for global air travel rose 5.9 per cent in April, but the picture is mixed going into what is traditionally the strongest part of the year for airlines in the northern hemisphere, a leading industry body said on Thursday.

While low oil prices are helping to keep prices down, the strong US dollar may hurt demand in some places, the International Air Transport Association said in its regular monthly passenger traffic update on Thursday.

"And it remains to be seen how long robust travel demand can stand up in the face of a trio of bad economic news: unexpectedly poor first quarter performance in the US, continuing weakness in the Eurozone and slowing regional trade in Asia Pacific," IATA Director General Tony Tyler said in a statement.

Capacity rose 6.1 per cent and load factors fell 0.1 percentage points to 79.4 per cent in April, IATA said.

IATA earlier gave monthly figures for air freight demand, showing momentum was slowing.

The association holds its annual meeting from June 7-9 in Miami and will give an updated forecast for airlines'profitability on Monday.