* 24-hour walkouts can no longer be ruled out
* Fourth round of talks to start on Jan. 24
* IG Metall demands 6 pct more pay, shorter working hours (Adds quote from regional IG Metall head)
FRANKFURT, Jan 18 (Reuters) - Some 44,000 German workers at companies including Mercedes maker Daimler and automotive supplier Bosch took part in industrial action on Thursday as powerful labour union IG Metall and employers held regional wage talks.
Citing robust German economic growth and record low joblessness, IG Metall union is demanding 6 percent more pay for 3.9 million metals and engineering workers across Germany.
It has also embarked on its first major campaign for shorter working hours in more than three decades, demanding that workers gain the right to reduce their weekly hours to 28 from 35 to care for children or elderly or sick relatives, and then return to full-time employment after two years.
Employers have so far offered a 2 percent pay rise plus a one-off 200-euro ($239) payment in the first quarter. They have rejected demands for a shorter working week unless hours could be increased temporarily so as not to put output at risk.
Three rounds of regional talks have failed to result in agreement.
"A further escalation of the conflict with 24-hour warning strikes can therefore no longer be ruled out," said Knut Giesler, head of IG Metall in North Rhine-Westphalia, Germany's most populous state.
He said that employers had not presented an improved pay offer and even refused to talk about working-hour reductions as outlined by the union.
"However, IG Metall will not come out of these talks without presenting solutions for the whole set of demands."
A fourth round of talks begins in the southwestern state of Baden-Wuerttemberg, home to Daimler and sports car maker Porsche, on Jan. 24. Any deal in Baden-Wuerttemberg would typically be applied in other states as well.
If the two sides remain at loggerheads, IG Metall's leadership may decide at a meeting on Jan. 26 to call for 24-hour walkouts or ballot the union's members for extended strikes.
More than half a million workers at hundreds of metals and engineering companies have taken part in industrial action this month to support IG Metall's wage claim.
On Thursday, as talks were held in North Rhine-Westphalia, Germany's industrial heartland, some 4,000 workers at Daimler near Stuttgart downed their tools, and over 1,000 employees of Bosch in the Bavarian town of Ansbach took action.
Forklift truck maker Jungheinrich, Thyssenkrupp's System Engineering and elevator businesses and premium carmaker BMW were also among the nearly 200 companies affected.
Such industrial action is common in Germany during sector-wide pay negotiations, and similar walkouts took place in 2016 and 2015. (Reporting by Maria Sheahan; Additional reporting by Christoph Steitz; Editing by Mark Heinrich)