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* FTSE 100, FTSE 250 down 0.4% each

May 21 (Reuters) - London stocks opened lower on Tuesday, tracking weakness in Asian markets as U.S. Federal Reserve officials maintained a cautious stance on inflation, while gains in AstraZeneca capped declines.

The blue-chip FTSE 100 fell 0.4% to 8,390.38 points as of 7:06 GMT, set for its worst day in over a month. The mid-cap FTSE 250 also dropped 0.4%.

Investor optimism waned as Fed officials hesitated to declare that inflation is on track to meet the central bank's target on Monday. This reticence also nudged commodity prices lower.

Traders also held back from placing big bets as they awaited insights from Bank of England Governor Andrew Bailey, due later in the day, and domestic consumer prices (CPI) due on Wednesday.

Focus this week will also be on Nvidia's quarterly results as it is expected to influence the broader markets given the euphoria around artificial intelligence.

AstraZeneca gained 1.2% after the pharmaceuticals giant said it expects to deliver $80 billion in total revenue by 2030.

Dowlais Group fell 5.1% and was the top loser on the mid-cap index after the GKN automotive owner warned of lower revenue in 2024. (Reporting by Pranav Kashyap in Bengaluru; Editing by Varun H K)