The blue-chip index was flat by 0843 GMT, with its exporter stocks also taking a hit from gains in sterling ahead of UK general election later this week.
The FTSE 250 midcap index was down 0.2pc, with Tullow Oil single-handedly accounting for the index's fall in early deals.
The oil and gas explorer was set to lose nearly half of its market value, or 1 billion pounds ($1.28 billion), as it tumbled to its lowest in nearly 19 years after scrapping dividend and announcing the CEO's exit.
Rival Premier Oil also fell 9pc on the FTSE 250.
Other news related moves saw Tesco top the bluechip index with a 5.1pc rise after the retailer started a review of its operations in Thailand and Malaysia.
Meanwhile, China's exports in November shrank for the fourth consecutive month, fanning worries over the impact of Sino-US trade war on the world's second-largest economy, overshadowing Friday's strong US jobs data.
"The contrasting US and Chinese data should swing the trade negotiation pendulum back to neutral from the Chinese side amongst the world's trade watchers," OANDA analyst Jeffrey Halley said.
Investors were also trying to size up the chances of a new round of US tariffs on $156 billion worth of Chinese goods from Dec. 15.
While signs of progress in the trade negotiations lifted the FTSE 100 to its biggest one-day gain since July on Friday, the bourse still recorded its steepest weekly fall after contradictory messages from US President Donald Trump earlier on.
"More soothing noises on the negotiations emerged from Washington DC on Friday, but one gets the sense that this Sunday's next round of tariffs on China is no longer the line in the sand it once was perceived to be," Halley said.
On Monday, some of UK's more domestically-exposed firms outperformed as investors bet on Boris Johnson-led Conservatives to win the election this week and deliver Brexit. Lloyds and Barclays were among the biggest boosts by 0848 GMT.
"Three days to polling day and the polls are looking good for Boris Johnson...although the spectre of tactical voting still lingers," Raymond James analyst Chris Bailey said.