US manufacturing activity expanded slightly in December after contracting the previous month, the ISM monthly survey showed on Monday. The Institute for Supply Management's manufacturing sector index rose to 50.7 last month from 49.5 in November, with 50 the break-even line between growth and contraction. The index has hovered around that line for the past six months, the ISM said, reflecting weakness in both US and global economic growth. Only seven of 18 manufacturing industries covered in the ISM survey actually reported growth in the month, and overall production growth slowed. But the employment sub-index rose to 52.7 from 48.4, showing the industry returned to hiring at a modest clip in December.