TRIPOLI, Libya — A series of NATO airstrikes targeted sites around Tripoli early Monday, following a day of heavy bombardment around the Libyan capital.

The airstrikes' increasing frequency has put ever more pressure on the beleaguered regime of Moammar Gadhafi.

The overnight strikes appeared to target sites on Tripoli's outskirts. It wasn't immediately clear what they targeted — Libyan government officials were not available for comment. They followed pounding explosions that shook Tripoli on Sunday.

A NATO statement said those strikes hit missile storage areas and launchers, command and control facilities and a radar system.

NATO military craft appear to be increasing the frequency of their strikes around the Libyan capital — the stronghold of Gadhafi's four-decade-old regime.

It adds more pressure on a regime that is already shaken by a four-month-old rebel insurgency, as well as several defections and a naval blockade.